Plumbing 1.5 drain line

I have a friend who's running 1.5" abs drain pipe from the second story bathroom to the basement with three fixtures on it. The three fixtures are bath tub, the sink, and the kitchen sink all tied into the 1 1/2 drain. The drain run is 25 feet plus he plans on puttinig in a drain vent for it. He dosnt want to re tie into the three inch stack thats into the bathroom all readily because two of the floor joist have been badly notched. I told him to sister them and re drill holes into them and tie back into the main Three inch stack in the bathroom instead of going through all that trouble. He worried if he sisters them and drills new holes he'll end up taking more wood out of the old joist.

You have two problems.
1. Drilling the joists, which is not a problem if done correctly
2. Him using a 1.5" drain line in the first place.