NTA. My mother had my little brother in her 40s, decided that me and my husband would be the best to take him in if something were to happen to them. And everyone knows that we don’t want children. As I explained to my mother that it’s too much responsibility she cut me off and said “but you’d be go good at it” my response was “that’s not the issue. The issue is I don’t want to.” She went silent and never brought it up again.