My brother and his wife both have significant mental illnesses that at times impair their ability to parent. It was very bad for a few years but as the kids have gotten older, everything has settled a lot over the past couple years and they are all far more stable. The boys are now 8 and 10. Due to their situation, my parents and I have done a great deal of childcare (taking the kids for weeks at a time) as well as ensuring the have food etc. The kids for years had bedrooms with their stuff at both my house and my parents house. I have been part of their life on a weekly basis since birth.
They recently told me that they had done their wills and chosen by other brother as the children's guardian. my other brother lives a 5 hour flight away and has for almost 2 decades. He typically visits once a year but goes occasionally send them cards and will face time them now and then - he isn't a stranger but he isn't close to them.
I didn't let on it bothered me in the least. It is their decision to make and the chance of them both dying is much lower now than it was in years past but after all the time and money and resources and effort....I was hurt. On the plus side, I get a close relationship with them that my other brother doesn't have but still!
They are someone resentful of having needed so much help. So I don't know if that is part of it - or if it is due to the slightly different political / faith based beliefs I have vs them (nothing extreme) or if they just really think there is something about him that would make him great. I'll get over it, but I am definitely stewing a bit at the moment.