Peach and nectarine trees

Can't help, sorry, but your question's in the right place and welcome to the forums.

Peach trees really don't require regular pruning like apples. What you do need to remove are any crossed branches, branches growing too close together, excessive suckers/water sprouts (yes, peaches get these at times), damaged ones, etc. If you feel the foliage is still too thick, then carefully judge where best to remove one whole branch at a time rather than do lots of snipping everywhere. It would only take a few branches to open the tree up (just don't take off the largest branches  )

If you're still not confident, get hold of a pruning book, perhaps at the library.