NXP won't be fast enough.. Pulse Width min =10nS typ @15V from spec.
There are two general uses of one shots.
1. Pulse stretchers
2. Edge detectors.
Since you indicated the spec is "2-5 Ns" (2~5 nsec),
my guess is you want the 2nd category.
Edge detectors can be made in many ways but you must realize when you are generating nsec pulse widths, you need controlled impedance driver , controlled impedance delay line and controlled impedance output.. ECL is one such solution (50Ω)
Can you please define your Driver source and load for this pulse?