I am finishing my basement which will include a full bath (toilet, sink and shower) underneath a sunken family room.  Rather than cutting through my basement slab for the drainwork, I am installing a SaniFlo mascerating pump.  My problem is that in order to get the appropriate drainage pitch for the shower I need to build it on a 9″ platform which will only leave me with a shower height of 6’3″.  In order to gain more height in the 42″x42″ shower, I am interested in removing part of 2 joists supporting the floor above.  In order to do this I understand that I will need to sister 2×12’s to the adjacent remaining full joists (on either side of those I intend to cut) and installing doubled 2×12’s perpendicular to the full joists with joist hangers which will support the cut ends of the joists I am partially removing.  –  I suspect there is a proper term for what I am describing above, but I don’t know what it is.

Are there any do’s and don’ts in doing the above work?  Can you direct me to a “how-to” reference or provide me with any advice?  –  I have a friend who is an experienced framer helping me, but I thought I would get a jump on the know how prior to doing the work this weekend.

Thanks in advance for any help you can provid!