Seeking serious advice , I’m torn

I have a dilemma need some advice I’ve had my sister’s son since June she decided she didn’t want him Anymore I have all of his belongings from her house but we never filled out any paperwork she knows I’m moving this weekend and she decides she doesn’t want me to take her son with me at the last minute but she also has yet to return from a vacation that she told me she’d be back from to get him on July 22 .... so now she wants me to take him to her neighbor who is a meth head and leave him there till she comes back from vacation whenever that is and it isn’t sitting right wit me anyone been in a situation like this and could give me advice that doesn’t lead to dealing with the law? I just can’t imagine dropping off my 4 month old nephew to someone who doesn’t have all

Of her children 😖