Newly Adopted Dog sits at end of walks and refuses to move

My wife and I adopted a 2 year old Pyrenees mix about 1.5 weeks ago named Tank. He is such a good dog, so sweet and kind. He’s well house trained. He pulls some on walks, which we are working on and may do some training sessions with an actual trainer. A few days ago though Tank would sit at the end of walks and refuse to come in our apartment building. We could coax him at first with positive energy, then had to use treats, and now cheese. We do not give him anything until he is in our actual apartment. When he sits though, sometimes he refuses to move and I’m worried he won’t respond to cheese soon. Especially when he walks with my wife, I don’t know what to do to get him in the building. Any help would be greatly appreciated! Thanks!