@Soupe du jour
I could press for stricter boundaries, but the issue is that my dad holds the only bit of relative power I care about, access to my mother, and he will not hesitate to deny me access if he feels slighted. My mother, despite me laying it out that these are not the actions of an emotionally healthy man, will not engage the issue, citing her ill health, reliance on him and fear of him spiting her for petty reasons too.

My cousin, despite the fact my dad doesn't particularly like the man, gives my dad an in to be nosy and critique my life down to the minutiae. If I object, he won't have a problem spiting me and/or my mother for the crime of not giving him "access" to detail my "inadequacies" to my face.

The ball is very much in my mom's court. As it stands, I can tolerate my dad's intrusions into my life and have some semblance of a relationship with her or I can cut him off and end up cutting her out of my life by extension.