Isis.....I know who you are referring to and it IS a problem when a wife is somewhat jealous or possessive of her husband to the point of not wanting to share him with his family.
There really isn't anything you can do about it other than hope the family member notices on their own and makes the changes.
Since only my kids post on here.....this is the problem. My oldest son has a few individual things he has always done with Isis and Sn00py, mainly Sn00py, as a surrogate father. His wife now feels the need to 'accompany' them instead of letting him spend the time with the kids alone. It's only a few times a year....like the Monster Truck Pulls coming up. I can't see why a pregnant woman wants to go in the first place. Sn00py isn't even looking forward to it now.
I don't know whether to mention it to her or just let it go.