Most Helpful Girl
Talk to him about it and say you love that he still wants contact with his daughter and you are thrilled that he's so involved in her life but you'd like to give her more stability. Being a strange house with a strange person can be scary to a little kid and you're worried she's not enjoying her time as much as she could. Maybe there's a way you guys can go half and half on a hotel room or he can stay at his parents' house for the weekend? Be open and nonconfrontational and see what happens.