Cooking up a Gravity Falls x Atla Au in which Ford and Stan are both earth benders but Ford is more proficient in metal bending and an inventor living in Zaofu while Stan is great in lava bending and a former pro-bending fighter. Dipper is a waterbender and Mabel could either be a fire bender or a non bender.
Ngl but Dipper being an earth bender makes sense considering I was thinking that Stan and Ford's dad is a fire bender and their mom an earth bender. This would make Shermie (Dipper & Mabel's grandfather and Stan & Ford's brother), a fire bender who married a non bender and had a fire bending son. However, I was also thinking that maybe Dipper and Mabel's dad married a water bender, which led to Dipper having water bending abilities and Mabel having fire bending abilities. Eitherway, I love your idea!