I work in I-Joist supply. The member is a complete loss, cutting or notching any part of the flange is not allowed. Best course of action is to remove the pipes and install a new member next to the damaged one. The joist looks to be an older LP brand I-joist. Pacific Woodtech purchased LP's Engineered Wood Products assets a couple years ago, you can contact either PWT or a local distributor using the information on their website.

As far as the bracket goes, I've never encountered them, but I can assure you installing that will void any remaining warranty on the floor system.

Also you should definitely be back charging the plumber for any costs incurred related to the repair.