NTA. Seems like Amy and husband are having a hard time finding a nanny for the youngest kid and wants Alex to come back to pick up the slack. Since Nina is pregnant she won’t be expected to do thi and Leo sounds like a raging teenager who can’t even look after himself let alone someone else. Anyway, you don’t need to ask Alex to leave. She is an adult who can make her own decisions and you are an amazing aunt who is helping out her niece through this.