Water onnection under the bathroom sink

The PEX lines should have standard "swivel joints" at the faucet which just unscrew counter-clockwise as noted above. Use channel lock pliers if needed. Where exactly is the leaking? If at the swivel joints, you could try just replacing the washers/seals in them.

I wouldn't cut anything as it can be a lot more work to re-install fittings afterwards. Nothing in there should be glued. Maybe a photo would help.