I had a mallard rescue duck. She stayed several months. They are not good at flying right a way and have to build up wing strength first by practicing. Best for now would be to give access to an outdoor, but enclosed back yard. They will fly out, but they will also fly back in. The first time my wild duck flew was with a crash landing on the roof. Then she called me like something killed her. Only to see her walk up and down on the roof trying to figure out how to get back down. It was hilarious. They will need a pool to practice their swimming and even to sleep in the water. Let them fly over the property, because that is how they learn about the area. Eventually they will fly away when it is time for them. Just don't rush it, they will know when it is right for them. Be prepared that they may stay for up to 4 months.