They are supposed to cap at 20 but honestly that's kind of funny and I'm inclined to leave it - it doesn't actually break anything aside from having skills that high basically rendering it impossible to ever fail a check. You would have to do a LOT of grinding to actually make use of stats that high.
*edit* I am curious about what their main stat screen looks like, the bars must be going off the screen!
*edit 2* actually there may be some kind of bug here, looking into the code it doesn't seem like it should be possible to stack modifiers to get caps that high without incredibly high base stats (which are set when the character is created and never change). Can you upload your save again so I can take a look at what might be going on?