plumbers,carpenters, need some help

Yup. cut out all that is rotted. Even cut the rotted part of the floor joists. Use a saws all, (reciprocating saw for the educated),. Scab a new piece of floor joist to the old joist. Use screws to do this, it's easier than nails. Then install new flooring layers as required to get back to floor height. It's not that hard of a job, just takes time. Remember to always catch half a joist with each side of your patch.

Jack