You are going to have to get all the rotted lumber out no matter what. The photo looks really bad. In that spot, probably the siding and sheathing are the only things holding your floor up. Without really seeing it, sounds like you are looking at tearing out the floor from the top, temporarily supporting the old joists from below where possible (temp beam) where possible, maybe work on 8-10 feet at a time, tear out all the bad stuff, and reframe. Probably sister new pressure treated joists to the old ones. Depending on dead load calculations, they may have a few or more feet of space where they are sistered. A structural engineer and a framing contractor should look at it, and you should follow their recommendations, if you are concerned what a home inspector might think. There is a chapter in my remodeling book, "Psychotic Remodeling," where a pregnant woman goes to bed and wakes up when an entire end of the floor falls into the crawlspace in the middle of the night. Their floor was not as bad as yours. Also, you may need to consider venting that space, looks like it is not properly vented.