91 Grand Marquis, had two spare keys made, they work in door, not in ignition.?

if they were cut from your original ignition key then take a wire brush and brush the hill/valleys of the key down -sometimes they have burrs that stand up and prevent the key from functioning properly--still no joy?--take them back and use another place to have the keys made--I have had the same problem in the past--some cutters work differently than others--might try an actual locksmiths shop-=-little more expensive but they cut til it fits and works

with a lot of cars back then you had a different key for the ignition then for the door locks. also it could be that the ignition lock has been changed having to use a different key.

Probably not cut properly or they used the wrong key fob. Compare the copies to the original, you're bound to spot something different between them.