How to treat joist that has wet rot before sistering a new joist to it
In terms of sistering you don't need to treat the joist there if it has dried just sister the joists and attach the new subfloor to the new joists.
Pressure treated wood for joists and subfloor is going about this wrong. If those get wet from above things have already gone awry. If you end up with another leak in the future you'll still need to pull up everything to determine the extent of the damage.
If you are planning tile above the subfloor invest in a waterproofing system like schluter ditra as well as a good waterproofing system in the tub/shower area. Other systems are available as well.