How to reinforce a joist with plumbing running through it?
I had an electrician notch the top 5&quot; of a 2x10 (9&quot; old growth Douglas fir) in the middle of an 18' span.
I brought in a structural engineer and he said the 18' 2x10 was already over current span code limits without the 5&quot; notch.  He specified 3/4&quot; continuous ply gussets nailed to each side of the joist extending 18&quot; past each side of the notch.  He allowed the gussets to only be the 4&quot; height and fit under the notch.
In your case, you are not in the middle span, I assume this is the start of the joist?
The toilet rough in appears to have completely cut through the joist so there is no connection and it has been blocked to the side joist with a single 2x4 and a single nail.
You likely want to get a structural engineer to specify a prescriptive fix for this.  A site visit and prescription is likely to cost less than $1,000 and be well worth it.
You might be able to sister with steel that is shallow and could sit above and below the plumbing penetrations and not need to be sistered the full length of the joist.