What I already searched: I honestly have no idea what to search for. I only want to see if my understanding/idea of how things happen is possible/realistic.
The situation :
I have two children (both boys), born abroad to british citizens (both parents are only a quarter british by blood but they were both born in the UK before 1983). So it is my understanding that the kids are both british citizens (since they were born to a british father married to their mother).
First question : Is my understanding of everybody's nationality correct ? I extensively researched that aspect of it (wikipedia and official websites) so it should be but better safe than sorry.
The boys have spent all of their life abroad (anywhere in the world : their parents travel around a lot and could either take them along or have some kind of "house base" somewhere, I'm not picky), with only a few trips to the UK for holidays.
In 1983 (the boys are 4 and 11yo), the parents both die quite suddenly (plane crash or something). The kids are both now orphans.
Their maternal grand-mother is still alive (66yo) but she is very sick (Angina Pectoris - she will die a couple of years later) and not physically able to care for two young children.
Their maternal uncle is unfit to raise them (not parent material despite loving his nefews) and has no interest in doing so.
They have an older brother (21yo at the time of their parents' death) who is living in the UK and in the middle of his studies at Oxford. He is a bit young to take care of his two brothers and it would mean stopping his studies. Although money would not be a problem as their parents were very wealthy and they inherited everything (divided into 3 equal parts and placed into trust funds for the two younger ones, to be inherited at their majority).
Finally their parents have both left a will saying that in the case of their death, they wanted a couple of friends (British citizens, married, both btw 45 and 50yo and perfectly respectable) to get guardianship of their sons until their majority. The friends know about this and are willing to do it. All remaining relatives have no problem with it and won't contest the decision.
Second question : Is it realistic to assume there would be no problem with the couple of friends getting guardianship of the boys ?
At the time of their parent's death, the boys are living somewhere abroad (again, anywhere in the world) and are currently under the guardianship of their "babysitter" (who is not a live-in nanny exactly but someone who is hired for the week and come to stay at the house while the parents are away).
Third question : What would happen to the boys in the time between the death of their parents and being placed under their new guardians' care (I assume they would remain with their babysitter, at home, if she is ok with that) ?
The new foster parents would fly to pick the boys up as soon as they learn and bring them back with them to the UK once everything is in order. How long would it take ? What would the procedure be ?
Fourth (and final) question : A few years later (1987, the boys are 8 and 15 yo), the foster parents decide to adopt the kids. Is this possible ? How long would it take ? What would the procedure be ? Can they change the kids' last name to theirs (once again, all relatives are ok with it) ?
Thanks a lot to everyone !