Something interesting and insightful re: bodyswapping and siblings from the Gravity Falls guy:
In this season we tackle a body-swapping episode. Body swap has been done a million times, but to see Dipper and Mabel, who are so different, given their worst nightmare of being in each other’s bodies-it was too fun from a character aspect to pass up. I think we get maximum fun out of that premise. For example, a body-swap episode is always “My life is harder.” “No my life is harder.” “Let’s find out!” “I learned a lesson.” Our theme isn’t that. It has to do with Dipper and Mabel being too tangled in each other’s lives and having to figure out what that means. It relates to them having to share a room. We take the discomfort of having to share a room and push it further into the discomfort of sharing a body. We’re able to, I think, do something a little different with it than you’ve seen before.
Alex Hirsch interview