Ewww!

ex lover and family member? Creepy.

She has given her feelings a higher priority than yours.

She doesn't want to feel guilty about excluding him. She doesn't want to explain to other family members why he is being excluded. That would be awkward. She wants to avoid any bad feelings. So, she takes it out on you. She isn't "fighting for his justice", she is trying to distance herself from her actions and the consequences.

Ultimately, he is the ex and you are the husband. She is more concerned with making him feel welcome than making you feel secure and valued. You are totally justified in feeling threatened. Not only by his smug behaviour, but also by her trivializing your objections.