Hey Derek, Geoff, 
Would like to join with the others in welcoming you to the Wags' site -- a fine passel of co-conspirators, not to mention, fanatics!  We really do appreciate getting some input re. the cast iron cookware from other places/traditions!
And reciprocally, wouldn't mind having the listing for the IDOS(which everyone else but me seems to already know about) -- & if you could btw. find a way to add another 10 hours in the day(or sum such -- that can't be used for more socially productive squeezing) would also appreciate!
Would also like to thank Roger for the 'heads up' as otherwise would likely have missed this quite interesting post, & second him re. that wonderful history, Geoff!  How often do we get anything remotely like your info?!
And Michelle, would like to join with Perry re. that 'multiple pic posting thing' -- should you ever decided to 're-tutor'!
Generally agree with most of what has already been mentioned, with just a few asides:

1) Along with everyone else, also feel that your COs are fairly old -- possibly, to my feeling, around the 1860s, with maybe a 20yr period to each side.

a) The sides of the COs seem fairly 'strong'/massive/squared-off, with sharp, not rounded edges at the bottom -- so likely earlier.

b) As Troy noted, the non-round/conical legs are often a sign of something being 'older'. 
Perhaps because early-on these things, tho functional objects, were more 'dear' -- if only a few in a lifetime were bought(& expected to last for generations), somehow more 'finess/effort' seems to have been put into the earlier pieces -- the 'feet' in the later/or more basic/crudely done pieces becoming progressively just 'pegs'. 
In this case, from what I can see, only the last(brownish one) eg. seems to be just a 'cone/peg' -- but maybe that's just the angle of viewing.

c)  The 'ears' are vertical(vs. the 'horizontal' later forms of the eg. Griswold & Wagner CO.s) but of 3 different forms -- one with a sharp '7', one with a bottom curve(generally thought to be later), & the 3rd completely solid. 
Have seen a simple shape of this last in quite new forms, where a 'bail hole' has simply been 'drilled thu' it -- but this hole is in the end, which argues that it wasn't drilled, but probably cast with a curved hole already in it, into which the bail was likely 'swaged'/hammered in -- & the 'expanded wedge form' has also been specially made to accommodate the vacancy of the vertical 'bail hole'(which, again, shows care)

d) Also, in at least the 2 'open' ear forms, they are a bit 'down'/below the top rim, on the side of the pan.  Frequently think that the lower down from the rim the ears are(like the handles on the early posnets/fireplace saucepots, & handed CO 'chicken fryers') the more likely the piece is to be older. 
It seems that it took awhile for people to realize that the lower the 'center of gravity'/ie. higher the tabs holding a bail/handle, the more stable the piece was -- why this is, I don't know.
So if we're into the 1800s, don't think that we're much towards the end.

e) If the round bottom bulge in the one oven is a 'sprue', it looks like there might be a 'smoothed/filed off' area at its top. 
As we use the terms, a 'sprue' is a round 'pontil-like' mark where the round 'funnel' for the molten iron was poured into the(often) upside-down mold-flask of the(here) CO(with the feet sticking up); while a 'gate' is the same 'funnel' but its having been squeezed so as to be 'long and thin', vs. 'round'. 
Because iron contracts as it 'freezes'/sets, there has to be more iron in the 'funnel' than just having it filled to the top of the mold, or with contraction, you'll wind up with a contraction-hole in the bottom of the pot.  But because when the iron finally does 'set', the iron in the 'funnel' does also, the excess has to be 'snapped off' from the bottom of the mold.
With the later, laterally compressed 'funnel' it was easy to 'snap off' the 1/8" wide 'gate'; while the sometimes up to 1/2"diam. earlier round 'sprue' took a tremendous amount of force to break it off -- sometimes taking the bottom of the pan(& all of the time/effort/expense) with it. 
While this was the reason for the evolution of the 'gate', the point here is, the great round mound at the bottom of this CO, may have been one accommodation to reinforcing the piece against the risk of breaking-off the sprue.

f) Up to 1840 Europe was ahead of the US in the tech. of casting iron; by around 1860 they were probably pretty much of a match; & by 1880(the 'High Industrial Revolution'), the US seems to have begun to lead the world -- likely do to a greater/more thorough integration of commercial finance, development, marketing(eg. the individual family stove etc. coming much later to the Continent, with a more traditional/mercantile-agrarian class system).
So it is possible that some of the features that were already superseded here in the US, were still quite viable in Europe -- so that our dating of when the 'sprue' transitioned to the 'bottom gate', & this to the 'side gate', may have come 20years or more later in Europe(without this being a case of obsolete 'holdovers'). 
So what might be features associated with ~1860 here, might be ~1880 in some place in Europe -- likely less England(which always focussed on 'function') than perhaps the 'Continent'.  But am still positing that at around 1860, we were more or less even.

2) Re. the lids -- 
a) I have 2 or 3 of these forms(but only the lids) with such 'stars' etc., & had unthinkingly considered them 'naturally' American -- undoubtedly, somehow pertaining to a post-colonial 'patriotism in iron'(like the well received English made export product to the former Colonies -- the 1790 16-star American Eagle wafer iron presumably commemorating the entry of the state of Tenn. into the Union).
But do think that Troy has a very good point, in that they might be French.  English & American forms tend to be somewhat stolid(like the functional/'business-end' bases of the COs)   But in addition to the circles mentioned by Troy, French forms can often have a fair amount of decorative design('Fleur-de-Lys, stars, etc.), which in an Anglo context, if they are not patriotic, would generally be considered 'frivolous'/non-utilitarian/effeminate -- ie. taboo -- esp. if they are small adornments, vs. eg. Penn Dutch symbolic forms.
But while I don't think of such design as English, perhaps that is just my cultural ignorance -- which Derek, & Geoff might be more familiar with.  Were there otherwise such 'stars' etc. delicate motifs coming from England into Australia in any media -- iron or otherwise? 
And, contrariwise, how much from eg. France got into Australia via either trade or immigration?

b) The early TDOs('True Dutch Ovens')/COs in both Europe and America had highly 'raised rim' lids, for the stabilization of the coals that would be put on top of them.  This seems to have remained the option here in the US for these(vs. the ordinary stove 'DO's/cookpots), while in France the 'raised rim' grew much smaller, tho is still present as a non-functional 'appendage' in their modern DOs(cf. Creuset)
[We used to say 'appendix', but it now seems that the appendix actually has a current vs. vestigial function -- to recolonize the colon with our 'good bacteria' after a purge of the 'Runs' -- Mmm!] 
But tho these are still completely functional COs, the lids seem to have hardly any 'raised rim' at all.  So is this simply just another trend in the French 'toolkit', or is it possibly an indication of what is really an Anglo(English or American) tech 'in transition'(as it were) -- from the CO, to the ordinary stove DO?  I dunno, but considering that these are all likely fairly old, the lack of a higher, presumably more functional rim on the lids is a bit strange.

c) Again re. the age -- 
As Troy, & Nollie, re. Glasscock, have pointed out, the amount of 'overlap' between when one tech. or style is initially superseded by another, & when the last example/vestige of the earlier form finally ends, can be vast.  Think of how long even Griswold, the leader in its field -- paired extra parts from different logos/styles together, apparently occasionally used an old pattern, or deliberately(I believe) employed an obsolete form/pattern for commissioned work.
However, by-and-large, the continuation of more-or-less non-competitive 'holdovers' because of the cost of 'retooling' is likely to be mostly limited to:
  i) Firms whose profit margin cannot easily afford the 'updating' cost, 
  ii) In markets/venues with enough of a restriction/protected niche that the 'new/better' products do either not have much 'penetration', or are a 'unjustifiable' cost to those on a restricted budget. 
Many of the CIC companies who were just 'getting by' without retooling, & were finally forced out by the 'Clean Air Act' of ~1950, were in this situation.
But these pieces are exquisite! -- not the mark of a firm holding on to its basic 'bread & butter', but likely catering to the 'high end' of the market(whatever that might be for CIC, at that time).
These lids are not only highly, & finely decorated, but seemingly thinly/finely cast -- not the mark of a firm in pain, but one, at least at this point, well able to deal with the market.  So I don't feel that these were made in small amounts produced over a long time, but more likely produced in whatever amounts, likely for something of an elite(Aristocrats, or well off Bourgeoisie) -- with production more likely curtailed by a change in tech., or fashion -- which in Europe, at least might have come with the advent of the 'Moderne', post ~1880 -- tho how fast the 'Traditional' was supplanted at the basic level of CIC, is a question.