Pictures would certainly help and I would be a bit concerned that sistering will help being these are the ends of the joists.

Two of them

Back up a little bit and take the pics again. Trying to see the system not just the rotten areas.

Not on site. Each joist spans 12’ over to a main beam.

That little bit of rot and mold isn't doing any significant structural damage. Make sure it's abated and forget about it please.

Have already sprayed it for mold. House is being sold and wanting to make sure it passes inspection.

You don't need to sister the entire joist. I'd add a 24" piece of joist on both sides of each joist and nail or screw the heck out of it.

It appears that the joist has settled somewhat due to the decay. It's not possible to know the extent or effect of the decay, so your safest bet is to sister the joist the full length from plate to girder. Something else might work fine--including doing nothing, but I can tell you from recent experience, if you're planning to sell the home at some point, a home inspector won't likely accept anything other than a full length sistering or a structural engineer's report that an alternative is equivalent.

As CRH Homes says and it is easier and cheaper to do it once correctly. You need (8) 12' 2 x 8's and $100 worth of galv bolts. Take the day and do it properly.

Are you saying sandwich the original joist????

Yes, if you sandwich the joist you'll double the bearing and you won't encourage the repaired joist to twist. I'd use screws long enough to go almost all the way through all 3 pieces, if you can get a drill driver in between the joists. Structural screws like the GRK fasteners sold at HD would work. It wouldn't hurt to buy a couple of tubes of urethane construction adhesive.

You might try using these ledger loks, since all inspectors seem to recognize them. and they are code compliant (for ledger board attachment). The instructions say to screw them in with a W-shaped pattern to ensure full attachment. https://www.homedepot.com/p/FastenMaster-3-5-8-in-LedgerLok-Coarse-Steel-Hex-Head-Ledger-Board-Fasteners-50-Pack-FMLL358-50/202268257

Bruce

I'm curious why the sill plate replacement project did not go further. That must have been expensive.

It's a good idea to sister the entire joist, or if possible, replace it.

Did so many repairs like this, existing joist will have to be jacked up to level the floor above and to fit the new joist over the plate since existing sagged a bit, other than that just sister the joist, apply glue along the top and nail into existing and you done. There is no need to sandwich anything like Charles said doing these "2' sandwich repairs" will only raise additional concerns.