Thank you! The easiest way to remove traits is by using MCCC (when you get to searching, just enter riv or founder, either of those will get it to show up) - that's how I've been doing it
Not sure how they got the founder trait though - I have nothing that'd automatically set them as a founder and the interaction doesn't work with toddlers, all I can think of that would've caused it is the riv_make_founder command.
It's not a dumb question at all! All I have within the mod itself for removing traits are the commands to clear an entire family / all families / add excA and none of those work in your case