@thegreenmeridian i come… with some more sources and possible non-answers because quite frankly it is history. (and i’m replying to op post bc… length mostly).
I’ll start with George McKinley Collins, or the possible ghost of. Basically, no proof exists of Georgey beyond his death. Him and Henry are 99% likely twins (as there’s no reason like with the Tozer family to assume that they delayed baptisms), born somewhere in 1818 (likely) and then baptised.(1)
That’s the only confirmed mentioned of George. Anywhere. It’s pretty easy to find the Collinses in the census, where they in 1841 happily show up with all their children, but not George. George also doesn’t go to Greenwich Hospital School. I got to dig through the entire box that contained Henry Foster’s admission, which had every person named Collins admitted (I assume 1728-1870 as on the Discovery description). Loads of Georges, loads of Henrys, no George McKinley. Henry was also a “this is very close on being too old for it” case, so if George went, he would’ve likely been in the same box. By 1829: no George McKinley, not at Greenwich at least.(2)
What I did find, with the speculation of “what if he just… died” because sadly, that’s what people just did, I went looking for Georges born around 1818 that died somewhere between that and 1829 and ended up with a George Collins who died in 1822 in Brighthelmston, Sussex, not all that far from Hastings. I’ve been unable to confirm if it’s him, because I only have a burial record and no one put a notice in the paper about this boy’s decease.(3)
Concluding, George McKinley did not go to Greenwich HS in 1829, nor did he live at home like Henry at 1841. It’s kind of likely that he somehow died in childhood.
Secondly, Samuel Dowbiggin, who didn’t really get mentioned in the OP post but alas, here he is, since there is a connection to the Collinses, though it doesn’t necessarily explain why Henry would leave his estate to him.(4) It’s indeed Major Samuel Dowbiggin, of Porchester Terrace, Bayswater (London, England).(5)
Ancestry has him in the 1861 census, which I happily looked at, first to confirm it was him, then to see if it was the mention you made of a census.(6) Also in that census is a Margaret F. Collins (29 y/o), Lady Servant, born in Ireland, aka Henry’s sister Maggie Foster.(7)
So basically, the connection so far is that Margaret likely went from living with her parents to living with Dowbiggin as a servant.(8) The odd problem is that at that point, Margaret is anywhere from 12 (1861 census) to 15 (1841 census) years old (please note that early censuses were known for being inaccurate), which makes Collins giving his estate to Dowbiggin just by that connection odd (as it may not have existed yet), but I guess there is just some earlier connection between the two families (or just Samuel and Henry) that isn’t known – there’s a lot of Henry’s past that we have no idea about.
Thanking @thomasblanky for rapidly answering my vague shouts about the Collins’ family whilst I was searching since I don’t know everything off the top of my head (and also for digging up some of these docs in the first place). Sources under the cut: