Niece joining us?

I am 20, husband 30, niece I have never met her before but guess she is 16.

Husband, who is otherwise a nice guy, has planned alone that his niece is staying with us in our apartment we rented for our honeymoon through our enite stay.

I don’t know what to do.

Says she going to help us with kids etc, but even that no because she is very young, doesn’t have he experience and doesn’t talk the same language as our daughter.