I would be the brother in law in this situation. My sister isn't married but she and her boyfriend have been together for so many years. At family gatherings I do talk to him a lot. We have similar personalities and he's kind of shy and my family can be a bit much. So in the beginning I was just trying to make him feel included so my sis wouldn't think we were ignoring or didn't like him. Plus my sister brings him to every single thing we have. They are always together. I have invited him out, I call him on his birthday, he calls me on mine (me and my sister are twins so I'm sure my sister makes him call lol) At family gatherings he makes a beeline for me because he knows I don't like to help out and my sister is always volunteering for things. Lol I feel like we are friends (not family since she doesn't have a ring yet but that's another story)
But anyway my sister likes that we get along so well and my feelings would be hurt if he said he felt uncomfortable with how much I talk to him and I would probably be like fine then I won't talk to him at all. But I guess everyone's family is different.