u/Green_MoneyMan325

I bought a property and had the contractor do the flip. I ask them sister the floor joist under the bathroom because sensed the floor was weak. Fast forward two years, tile starts to crack I rip out drywall of room built under bathroom to see the images below. The floor is sagging and decaying floor joists still there. I need guidance to fix this myself. Don’t have money to hire someone right now. My thought is (order of operations): (1) the pipes need to be redirected or lowered? (2) Rip out bathroom floor? (3) Then new floor joist? (4) Then redo bathroom floor?

Am I right? best way to do this? Please share guidance on best practice to ensure the structural integrity of the floor.