Rottmnt headcanons screw it-
My apologies if this information is off somehow
Donnie used to read to all his brothers when they were younger but now he just reads to mikey(he specifically buys books for donnie to read to him)
The boys created a "watchlist" that dictates what isn't allowed in the lair to have/say because it affects one of them (peanut butter because raph's allergic, certain items because there texture upset donnie, there are certain phrases on it as well)
There money comes from selling stuff online or April(mostly Donnie selling smaller grade tech on the darkweb)
Raph, mikey, and Leo are the only one's who have seen/known of Donnie's sensory overloads and panic attacks, he trust April and Splinter but he doesn't want them to see him a vulnerable panicked mess
Whenever he has sensory overloads or panic attacks the 3 won't leave him alone until he's calmed down(which he appreciates) they'll go silent and keep the room quiet until he can stand it since sounds bother him the most(raph calls it "quiet time")
Mikey paints on everyone's shells/faces/arms, they never complain(don't even wash it off) so he still does it. The most response anyone gave on it was when Cassandra mentioned Leo's cool dragon "tattoo" and he just said "thanks".
Donnie doesn't paint his tech mikey does it for him.
Mikey actually could make some decent tech if he applied himself because of what he learned watching Donnie.
Leo soon learned everyone was joking when the say shut up because the one day he did they were extremely worried and were close to taking him to a human hospital.
Raph's seen Donnie and Leo at their lowest, they trusted their big brother to piece them back together when they fall apart
(Pretty much Canon) Donnie's love language is building things for his family, it's part of the reason he works so much, necessity is the mother of invention, to him, their needs and wants are the most important necessities
Edit: one more!
The disaster twins sleep the heaviest(when they actually do sleep), raph and mikey are light sleepers, if Leo or Donnie falls asleep somewhere that isn't a bed the boys will just throw a blanket on them and avoid that room til they wake up.