What's each of the Geminis' favorite thing in the world? What do they want that's out of reach (because of their living situation, their roles, their own limitations, etc)?
I mean, if you asked them, Leo would say "Donnie" and Donnie would say "Leo," but disregarding their dumb, sappy answers...
Donnie's favorite things are science, just as a concept, botany, his tech, his private 'library,' (boy owns so many books,) and his scarf.
He would love to have a garden one day but is currently not permitted to. He doesn't like relying on Leo for physical protection in the Nexus so often and wishes he had a hard shell to take the heavy hits sometimes. He hates always watching Leo physically throw himself in harm's way on his behalf. It's their system, and it works, but that doesn't mean Donnie always has to like it. He hates relying on Big Mama's healing staff to keep him healthy and functioning. He'd love to never see another doctor, nurse, or healing witch for as long as he lives. Right now he has to interact with them every day.
Leo's favorite things are stage magic, acting, piano, comic books, and his scarf.
He wants to know witchcraft, like Donnie and Mama do, but has never been given the chance to learn. He didn't 'show promise' like Donnie did. Even more than this, he wants to learn healing magick, or even just more advanced healing in general. He and Donnie are already both very competent medics, as they care for most of each other's injuries in the Nexus, but he wants to learn more. He wants Donnie to never have to see another doctor, nurse, or healing witch for as long as he lives. He wants to take care of it. But he hasn't been able to do this yet, and any time he asks for more resources, Mama tells him that 'she doesn't see why he would need all that.' He wants to protect Donnie, and it infuriates him every time he can't. Each time Donnie gets injured feels like a personal failure on his part.
To some extent, both of them privately want to get a chance to meet other people their own age and actually interact with them in a normal, genuine way. To, I dunno, to talk to people? To make friends, or something? To have a relationship with someone that's not based entirely off of reading off a mental script and achieving a means to an end?
But yet again-- that's a pretty stupid wish, isn't it? Why would they need that? They have each other. Obviously. And what kind of a brother would they be if they wished for more than that? They don't. They don't, not really...