I've lived with intact dogs in the same house many times. If you absolutely must do it during a heat cycle, go with two barriers at all times. One dog in crate behind a closed door. If you have kids in the house, make it 3 barriers. Both dogs in crates in separate rooms with a closed door in between. If possible, get one of them out of the house for the worst of it (depending on the dogs, it is about from day 10-14). With our intact males, they would go from nuts to completely insane when "the change" takes place. At 9 mo you don't know when she'll come in the first time. Talk to your vet about possible options. There are medicines to avoid heat cycles, or change when it happens but I don't know how safe they are or when you'd need to start (like if you could start the medicine after the heat cycle had already started).Â