
Many dogs will be sexually attracted by the smell of a pregnant bitch. She will also have some discharge towards the end of pregancy and he is no doubt checking ehr out in the hopes that she is going to be in season and ready for mating. It is doubtful he knows she is pregnant he just wants to ensure that no one else gets there before him, guarding a valuable resource.
The bitch understandably is ratty with him as she is uncomfortable, and just wants pesce to find a safe place to have her babies. You shopuld ensure that she has a safe place to whelp where other animals in the house have no access, and by now she hould be able to spend time there if she wishes and get away from your other dog.
He should be kept away from her and the pups until at least their eyes are open, and then be guided by her as to whether he will be allowed anywhere near them. Most bitches will not allow other dogs to interact with the pups until they are running about.
Once the pups are runninga around make sure that the adults can get away from them, especially the Dad, as many dogs find young pups frightening, as they tend to try and suckle at them, and if they have no clear escape route mugh try to hurt them.