Welcome back, Cajondy!
Very glad to hear that "real life" has loosened its grip a bit and given you some time to come and see what has been afoot at Pentrefoelas -- quite a bit to digest at one go.

As to
... HUGE apologies for the month's silence from me - personal circumstances have prohibited my being able to log on and access Rootschat until now
don't worry in the least; I meant it when I wrote
even when the New Post notifications are working ... , there can still be many wholly understandable reasons for a period of nil reaction on a thread; and I am entirely relaxed about that.
-- and "real life" imposes itself on us all from time to time.

As to
I've read, re-read and will need to further re-read to ensure I digest it all. ... I am determined to get to the bottom of the Hussey Burgh challenge
we'll be interested to hear your additional comments and questions once you have had the opportunity to absorb the latest info more fully. Hope you will agree that the ID of MHB's mother is now reasonably secure, albeit so far without much of a maternal line further back.
On the paternal side, we all know that it may never be possible to prove much, aside from the family tradition; but if you want to keep at it (bravo!), I suppose a reasonable "next move" would be to try and track down John Hamilton* HdB's family papers, on the off-chance that some evidence of support payments or an annuity (or simply tell-tale correspondence) might have survived. Even if not catalogued, they could still be sitting unnoticed in the old family solicitors' dusty cellar. First steps in that direction might be:
(1) a post asking for help on the main R/chat Irish board, setting out John's full details (incl. Burke's IFR 1976 etc), with a cross-ref. link to this thread;
(2) contact the Irish heritage centres local to his two houses;
(3) try to trace and contact his living descendants as disclosed in IFR 1976;
(4) find out whether an entry for a will in his name appears in the printed annual calendars of grants for the Dublin PPR. (If surviving, grant should disclose name of solicitor dealing with the matter -- can then use annual Law Lists to identify current successor firm; or approach Irish Law Society for advice/assistance via their internal practice succession records.)
If a will was made, key Q is, did it get safely preserved at a local registry -- or, more likely, go to the principal registry and get burnt in the Four Courts fire of 1922 (if so, talk to Irish National Archives in case a copy has been discovered and handed in to them, as per NAI's standing appeal to lawyers to try and re-constitute the lost records).
In your shoes I would also want to uncover more about Walter HdB's Russian trip in the early 1840s and Albert's birth there. Did John Hamilton* HdB come too? Could any passport or visa papers mention the names of accompanying servants? . . . et cetera. If you decide to go down that angle of attack too, just let me know; I can probably point you at some possible sources at Kew and Guildhall/LMA.
With luck other contributors may have different/better ideas for you to pursue.
Rol
* (not John
Hammond HdeB, as originally typed) --
Corrected 11.xii.10