Adopting

So my sister has had her children took off her and everyone wants me to get custody of them she's had twins they're 5 months old, I don't know what to do, I have trouble conceiving and me and my partner have only been together 2 and a half years and we don't know what to do. Just looking for advise if I'm honest we have no children but we're trying to conceive I don't have a clue what to do, part of me wants to do it and part of me doesn't know because if we want our own children it's going to be stressful as we will already have the twins😥