Turquoise is in the middle also unlike the other Gems, mine are suppose to be male but that wasn't an option so the are just genderless...
Diamond is telepathic and uses a then Katana like sword that can cause psionic disruptions, he comes off emotionless but is in fact very sensitive. He tries very hard to keep Emerald in line when he flies off the handle but often gets overwhelmed by Emerald's emotions and gives in. Diamond is very knowledgeable about a lot of things mostly earth culture.
Emerald is telekinetic with us powers being more on the physical side, his weapon is slightly bigger a long sword that he moves telekinetically during a fight. He likes action over communication, being frustrated with Diamond who like to talk about everything when fused it is the only time Emerald completely submits to Diamond. Emerald is an expert fighter in both hand-to-hand and also with all weapons.
Turquoise has a buster sword that can permanently wound gems and separate fused gems.
They were originally on earth during the battle but Rose sent them off world to look for some mythic artifact that was going to help her take down yellow diamond but they got lost in space. They look up to Garnet because they want to be fused all the time too as Turquoise but it is hard because they like being themselves and Turquoise is cynical and slightly nihilistic, so he ends up splitting them up which pisses off Emerald and he gets very angry and thinks it's because Diamond doesn't want to be with him and Diamond thinks it is his fault and then doesn't want to fuse because he feels guilty.