"Is it possible to replace only the rotted section of the sill plate?" ---- this is the rim joist. And the ends of those floor joists, and the diagonal sub-floor, and probably the bottom plates close to the doors that show water damage like this one.
This is a bigger job for an experienced DIY'er. Temporary beam and posts inside, right next to the brick foundation, remove siding to replace the rim joist after sliding new main joists in to sister next to old ones. Then, replace the dry rot sub-floor and wall bottom plate after temp. supporting the roof or second story area directly above if more than 3' wide. As you rebuild, fix the flashing alongside, over and under the doors which is why you get this work.
If the footing is wide enough, you may get by with making the temp. beam - permanent with pressure treated wood- not replacing only the main joists. (and solid blocking over the beam)
Be safe, Gary