i believe xion is going to pretty sociable in recolle! with her being a big youtuber and all that, so i could see frank being like 'let my kid help yours' if reigen is all [face in hands] about it! look, dads gotta stick together and he knows that raising kids is Hard Work

also, frank could a supportive neighbour and not give reigen any more beer after one but he will also probably think it's a blast and sometimes give reigen one or two more. throw salt in his face if you want him to stop or keep drinking, bud

(also also, imagine family bbqs)