GPS NOTAM'd as unreliable on a dark, moonless night?
Fly the ILS approach (or fly a visual approach along the track of the ILS approach backing up your visual with the radio signals). That will give you terrain and obstacle clearance all along the route using locally generated navigation signals that will be entirely unaffected by GPS jamming.
I would 100% (and have) take center's altimeter setting and fly the track of an ILS or localizer rather than "whelp, nothing can be done..." This was VMC; you don't need a local altimeter setting to be safe using the radio navaids; you would need it to legally fly the approach as an ILS approach.
It appears there were too many sources of confusion. GPS jamming, moonless night, busy ATC, not planning on VFR before takeoff, 20 minute short flight, instrument approach disabled, young pilots, mountains, and perhaps others.
Flight safety is about removing entropy and there were several steps which could have been taken, including not flying at all because of forced VFR on a moonless night near mountains.