So I read the final (so far) update, and it looks like OP's parents (who are divorced) discussed amongst themselves what to do if there were extra people, and that there was enough of a buffer with catering and tables. However, when dad called OP, he made it seem like he was asking to bring extra people and turned a nothing burger into a big something. It's been ironed out, but I'm starting to guess that lack of communication may be why OP's parents are exes. Also, he's not paying for the whole thing; both OP's parents and the fiance's parents are paying for the wedding and reception (in case anybody cared).
