Some random headcanon notes: Raph and Donnie trim and paint their claws. Those two also have very sharp teeth, unlike Leo n Mikey. Leo has the most upright posture of the brothers. Donnie is usually rather hunched and in general has terrible posture. Donnie n Mikey 10/10 shrimp brothers.
Mikey and Raph are a bit jumpy. Donnie almost always is listening to unreasonably loud music- though he will turn it down if someone is near him. Leo is a little bit quieter than he used to be but he still retains his quick-witted one liners and middle child-ness. His favorite person to annoy is Donnie- though it’s usually just in an attempt to get Donnie’s mind off work to have a laugh. It’s more successful than you’d think.
Mikey has picked up spray painting again and it stands as his current favorite pass-time. When he’s not hanging out with his brothers or making art, he’s hanging out around the city- usually with April. He frequently drags Raph along as well, just to get him out of the house. Raph is still quite weary of being out in public but he loves being able to go to restaurants and malls without needing a disguise.
IDK I might have more but that’s it for now :P