Crooked window sill in old wood house

OK guys, I believe I have opened up a can of worms. OK, this is what I have done. I removed the center window molding (between the 2 windows) outside to get a better look at what I am up against. THere is a 2" X 4" going from top to bottom, between the 2 windows. Where this 2" X 4" goes just below the sill, this 2 X 4 is all eaten up by termites (old damage). I took some photos of the bottom of the sill, showing the difference from one side to the other. I also took photos showing the bad 2 X 4 running between the windows. I also took a few photos showing the level on the inside top of the window frame, as well a the level on the window sill (way out)l. Inside the window frame (well, below) there are a couple of boards (solid) that are running parallel with the window sill. I believe that because the one board that is all eaten up by the termites, the inside boards have nothing to fasten to, so the entile window frame has shifted downwards on the left side. I am afraid that I am going to have to replace the eaten up 2" X 4", and then somehow raise the inside parallel boards, so that the sill is pushed upwards. Then nail the parallel boards to the new 2X4 to keep it from shifting again. If this is needed, I am hoping that I can do this from inside the house. I would hate to have to remove the clap-boards. I am assuming that it is the same case for the window on the left as well. However, I am hoping I can do this to one window at a time. The actual window frame is in pretty solid condidtion, except for one of the blind stops being rotten at the bottom. I am hoping that if I can remove just the left and top molding, I will be able to shim the window fram back into square, or at least much better than it is now.

Any ideas? Any advice on this? Any input you can give me will be GREATLY appreciated. Is my way of thinking correct, or is there a much better and easier way of doing this?

Below are some photo. I hope this helps.

jJim, I think we passed your , "easy" a while back. Now we're into ,"more involved". Not too bad, but more involved.
This will work without taking out the window.
I would remove all the plaster from below this section so you can work from the bottom up. Get some 2x6's and rip them to the correct size to match the current framing. Cut out the rotted 2x4's as square as possible and add a new piece to the rotted 2x4. You can use a mending plate to keep it in place. Then add a second 2x4 and sister the two together using 3" deck screws. The sistered 2x4 needs to be as high as possible so you can screw it together along a good distance. If you can fit it all the way to the top plate, do that. If you can throw a few nails in through the exterior siding into the new framing so much the better.
Rebuild the double 2x4's as needed below the window. You can screw up from the bottom to secure it.
Square the window in the opening, shimming the low corner. Add shims midway and at the other end if there's space under the window sill. Add shims between the side jamb and the rough framing and drive finish nails through the jamb sides and the shims. If the window is taller then 36" add two sets of shims at the 1/3 and 2/3 area.
That should be it. Insulate sheetrock and add the interior trim
Ron

Ron, there's a problem. I had already figured to get a P.T 2" X 6", and rip it to the correct size, but this area is where the sash weights go. If I sistered another 2X4 in its place, then the sash weights would not fit. I dug a bit deeper, and it seems that one side of the 2X4 is still solid. I don't know if this makes a difference or not. I thought that the window sill was supposed to rest on the parallel boards below the sill, but I checked another window I had done before(the center molding was still off on the inside), and I see these same boards below the sill, but they are not resting on them. Confusing for me.... Well, anyway, what exactly does the window sill rest on? Is there a support board that it rests on, that I can't see with the outside trim removed? Or, does the sill just float there, fastened to the lower edge of the window? If it is supposed to float, fastened to the window frame, then how about this. If I remove the inside and outside molding from the top, as well as the lower side, will the window frame be free enough to pry it upwards, long enough to tack a few boards from the top, to keep the opening square, then install the left molding to keep it square? After that is done, then the top molding can then be added back to hold the rest in place? Forgive my ignorance, but I guess what I really need to know is what the sill is supposed to rest on, if anything at all?

Tom, yes, there are weights for the windows. I know that there's is no big deal with removing the clap-boards, but here again, I keep thinking of that dern can of worms.:laughing: I am going to have to redo some of the plaster anyway, so removing the plaster for me is no big deal, it has to be done reguardless.