Home Improvement Questions? Ask a Handyman for Answers ASAP
Looking at the photo, I now understand your concern. The notches in those joists are so deep as to make the joists pointless - all they are doing is providing something to fix the flooring to, but they won't provide structural strength because they won't withstand any significant bending forces..
That depends on lots of things, like span, and what things are bearing on the joists. I might be possible to strengthen the joist(s) with a steel plate, but it might not. The routes of the various pipes need to be sorted out first, clearly.