Gosh this is something i think about often, particularly the Leo half, because these kids are MESSYYY
Like as fun as the fanon twin dynamic is, Leo is Donnies biggest bully. On one of my last rewatches i wrote down the times when they actively bullied Donnie and Leo was the one who targeted him most, followed by Mikey. The main difference between Leo n Mikey is that Mikeys feel more like him copying Leo because he looks up to Leo and wants to be like him, while Leos ones are just cuz Hes Like That
The amount of jokes about kicking Donnie out of the team or degrading Donnies tech (the later ones more common in early s1) stop being funny and become sad, because you can really see how much they affect Donnie and how much he masks around his brothers because of it. I dont think Leo means any of it, he is just projecting and trying to cope with his own issues, but his words and actions really do wound Donnie and we needa talk about this more!!
Thats why I ADORE Donnie and Aprils relationship- she never demands anything out of Donnie, she asks. She comforts him and is by his side and shes the only one who doesnt bully or belittke him- he gets to be 100% himself around her and its great. Mikeys the one who comes closest to Donnie being comfortable around when it comes to his own brothers but even then Mikey still makes "kick Donnie out of the team" jokes </3
Theyre so messy i love these stupid turtles