Why is one of my dogs sleeping in the other dogs igloo?

Hey everyone! My wife and I just recently adopted our second dog, named Scout. So far he has been an awesome dog. He is kind, easy going, and submissive. As is our 1st dog, BB. once we brought home Scout, we noticed that BB was showing some subtle signs of being territorial, which I think is mostly normal. She has already started to warm up to Scout, and hasn't been overly aggressive. However, with the addition of Scout we also bought another Igloo so that each dog could have their own igloo for sleeping/private time. We were hoping that BB would choose to stay in her igloo that she's had for months now, but we've noticed that she sneaks into Scouts igloo quite often, which forces Scout to sleep outside of his igloo. And he won't go into the other igloo (that's supposed to be BB's). I'm thinking that this is because she has "claimed" both igloos? Is there a constructive way that we can teach BB to stay in her one igloo? Right now she just kindof switches between the two, which confuses Scout. Or would it be ok to remove one of the igloos and have them sleep in the same one? (the second igloo could easily fit both dogs).

Any help would be appreciated.