how would I fix this?

hi! You shouldn't have to have any geometry under the second shirt, or it is bound to clip. Specially when you can't see it from any angle. So i would delete the under shirt.

And the other issue, i don't understand it quite. Have you edited the specular and bump map already?

Also, please refrain from posting pictures with naked sims. You can cut it out in imgur via editing. thank you!