My wife's brother is usually one of the most chill persons you could ever meet when we see him at events or restaurants etc. However when we're all gathered at my wife's mother's house for family events (Christmas being the most recent) he turns into a passive aggressive person. It's in very subtle ways but I pick up on it.

It's usually when I'm getting a good amount of attention from other family members or I'm appearing to be comfortable in their house. He will say or act in a way that shows hostility towards me in ways he knows only I will pick up. It goes unnoticed to other people. It doesn't necessarily create a chill environment for me which is all I want because family get togethers can be stressful by themselves.

When I asked my wife if her brother was going through some stuff as his reason for acting strange she said he likes to play the part of the grumpy person sometimes.

Bottom line I believe his alpha male position in the family unit is threatened by me and he looks for small ways to make me feel uncomfortable hence maintaining his position. Has anyone else here experienced this with a girlfriend or wife's family or do you have any knowledge to drop on how I can navigate this situation?