Parent Trap AU where Stan and Ford meet at summer camp, each having lived with a different parent.
Except in this one, the parents are Ma Pines and some random guy. When Stan and Ford switch places (Stan had started with Ma Pines, Ford lived with Dad Pines) and Ford went to Ma’s, there was some guy hanging around trying to marry her for her money. Filbrick.
Through a series of wacky events, everybody ends up back in New Jersey to undo the switch. Cue Ma and Dad Pines starting to fall in love (kind of) again. Filbrick gets insanely jealous and insists on Ma stop seeing them at once.
Ma agrees to go on the yearly camping trip she and Stan do, but now bringing along Ford and Filbrick. The young twins conspire to make him look like a fool all weekend, and it’s awesome. Ma finally kicks him to the curb when she realizes he tried threatening her babies.
Ma and random guy Dad Pines reunite and fall in actual love, and Stan and Ford discover what it’s really like being twins after not knowing the other existed for the first twelve or so years.
They’re their own people with interests and lives and friends but now they’re brothers and it’s all good.