I play the guitar as well so I can certainly relate. My nails are pretty thin and brittle and tend to crack a lot as well. I invested in nail polish that promotes strong and healthy nail growth. I also try to keep my nails cut low to avoid any chipping.
Have you tried fingertip picks that wrap around just above the first knuckle? I know you can get them for thumbs, but I seem to recall seeing them for the other fingers as well. It might save you a lot of distress in the long run!