How do you prop an exterior wall to replace rotted wood?
This shouldn't be too difficult since according to your post, the top plate is OK. You'll need to get a few floor jacks and support the top plate from the foundation. You can rent them at most home stores. The jacks can be a little out of plumb to replace your bottom plate but then straighten them up. I would just replace all the studs. It will be quicker than messing around trying to sister them. Studs are cheap, you'll probably need 5.