I am renovating a rental property. In the bathroom we have found severe wood rot in 1 of the 3 main ceiling joists. The rot goes through 2/3 of the joist (4 2x10 with 1x6 on each side) on the right side of the joist, approximately where the rot ends is the bathrooms vent pipe which is what makes this hard for me. Should I cut the rot straight out, replace the wood and sister on each side? Is that enough support? We have discussed interlocking the new wood with the old, bolting the wood, and adding a 4x4 post on each side of the vent pipe. Any input would be appreciated.