Sistering a split joist not code?
I may regret answering this question without first seeing a picture of the joist, but I’ll try. 

There is nothing in the Code about sistering joists. There are references to “alternate design methods “, which sistering joists would apply. (See ICC Section 2308.8.2)

I’d leave the split joist installed and add a new joist on each side of it. I doubt the joist has sagged much and could easily be jacked back into position without damaging plaster walls, cracking windows, etc.

The new joist should sit on the beam in the same manner as the damaged joist (minimum of 1 1/2” bearing) and installed in a matching hanger on the other end. 

In order to keep the new joists from possibly creating a squeaky floor, I’d use epoxy on top of the new joists. 

I’d glue the damaged joist together and install a splice on each side to hold the joist together. Nail with 16d at 24” o.c. Staggered each side. (It’s just to keep the old joist together. It’s not supporting anything anymore.)