Prior owners to our house had some repairs done and two floor joists were cut in half. Photo:

I'm planning to sister 2*8s to each of the cut joists, as well as some of the notched joists. Heck I might as well do every joist since the bathroom is only 96"*77". Is this an acceptable fix? I'm not sure what to do in the area around the toilet, but some framing obviously needs to be done. The pipes will hopefully be rerouted, or if need be a hole large enough for 1.5" pipe drilled through the center of several of the joists. Is this acceptable?

I'd also like to drop the level of the sub floor down about 1/2-3/4 of an inch. I was thinking I could make the new joists flush with the bottom of the original joists, and then plane the original ones down 1/2 an inch. Is this okay to do?

Thanks,

Gil