Concept seem familiar? It should, I "borrowed" it from the Phineas and Ferb movie.
Here we see Lisa and Maggie visiting their 2nd Dimension counterparts. Possibly singing. The 2nd Dimension being ruled over with an iron fist probably by an even more villainous version of Mr. Burns.
You'll notice that I added some extra features to Maggie-1, Lisa-2 and Maggie-2.
For Maggie-1 I added her teenage scar for no reason from Simpsons Fantasy VI
and Simpsons Fantasy VIII
For Lisa-2 and Maggie-2, I made them both paler, since they've never been outside much, and they're both wearing the same outfit to a certain degree, as well as being tagged, with those armbands under their sleeves.