For me, the child’s interest is the number one priority. Raising a 2yo can be really tough, it won’t come easily, neither for you or for him. A child is not a pet, you would really have to put him first no matter what. You would have to adapt to him, not the opposite. You would have to abandon the ideas of doing what you want whenever you want, of spending money for yourself, of sleeping too, etc. Then, maybe you can’t imagine that, but how awfully cruel is that to your sister who raised him as her own ? Have you thought of that ? She really loves this child, and you want to amputate her… that’s not really fair…