soo how can i add body groups to models that have flexes is it possible?

You make two of the same models, just with the mouth on different sides. The other Sonic gmod models do this. I don't know how you can make it into bodygroups, but I'm pretty sure that making two versions of the Fang model is the best method into having the mouth on the left and right.

yeah that be the way i probably will do it
like i say sonic mouths and eyelids are always weird to
work with