Jason has called the others a plethora of names since he came back, on a varying scale of insults (he still calls Tim "The Replacement", even though they're both very much over that now; he likes to think of it as an affectionate nickname, although he's not entirely sure Tim would agree with him).

One name he's never used for any of them (outside his own head and he's the only one who has to know anything about that) is "brother" (although he's called Cass his "sister" on more than one occasion, but he doesn't think too much about that).

He's getting closer to it every day though, especially when he hears Dick use it to refer to him as often as possible, as if he's trying to make sure Jason remembers.

Maybe it won't hurt as much as he fears it might do.