Don’t Like Or Trust Mom’s Boyfriend?

Something I’ve noticed over the past couple months is how often (still) our dogs bark at my mom’s boyfriend. My parents are getting a divorce, and it’s only me, my mom, and brother living at the house along with our 2 dogs (2.5 yr french bulldog, 7 yr mini dachshund) and 2 cats. My mom’s been dating this guy for a year now and he’s even stayed at the house for 2 months straight before. Personally, I don’t like him very much.

What was just brought to my attention was the fact that even after being around so often, even living in the same place, our dogs and cats want nothing to do with him. Our dogs usually bark at anyone who comes to the door, but once they recognize the person, they quiet down and leave them alone for the rest of their stay. However, this isn’t the case with the boyfriend. They bark when he first arrives, and eventually they settle down but it seems like they only tolerate his presence; they don’t go up to him expecting pats and seem to just grudgingly receive some attention from him, but they won’t sit on the couch with him or beg for food from him like they do with everyone else. If they see him emerge from another room, they’ll start barking at him again. Do they just not like or trust him after all this time, even after being exposed to him so much? My dad hasn’t been to the house in almost a year and they dogs wouldn’t leave him alone (affection-wise), even though he never went out of his way to pay them much attention. The frenchie hardly even knows him yet he was following him around like a lost puppy.