In my opinion, scabbing is okay, but I would only scab after encapsulating the rotten wood with some major paint. See, the rotten wood is highly absorbent, of even humidity, and ….well, you get the picture.
Additionally, scabbing is fine, but bolting into 3 inches isn’t wise, it’d be best to do nothing more than nail into weaker sections, bolts only weaken boards. On a different note, the bolts would be good where the wood is solid for both the scab and the rotten joists.
Also, for proper strength, I’d recommend scabbing no less than one third the distance of the major rot on either side, so for 2 feet of rot, a minimum of 6′ scab. Wood is cheap, the longer the better. The trouble is, there is probably a lot of stuff in the way. I can’t see from my computer. If the scabs aren’t all together in one area, they are glorified nailers.