I've got 2 nieces and 1 nephew. The nephew is technically not related to me (he's my BIL's son) but I've always tried to treat him as my own because to me he is. I have my nieces over to stay all the time and feel bad because I've never had the nephew over. Yesterday he told me he wants to come stay. It's tricky because he's in a 50/50 custody deal. My sister and BIL are not on good terms at all with the boy's mom either. I've thought about reaching out to the mom to see what she says but she's a stranger to me. My sister and BIL have always just done whatever they want and kept it a secret from her. So would you have your nephew over without the mom's permission? Is dad's permission enough? I live 2 hours from them all so it'd be for a few days.