If the wireless NICs are added (versus installed as purchased), check the antenna connection on the NIC.
A quick check would be to move the laptops close to the AP and see if they can connect. If so, then peel 'em and re-seat the antenna connection.
The connectors are so small and tight, it's frequently difficult to get them squarely on the mating connector (on the NIC pcb).
The two antenna cables are very thin, usually white and black. Work very carefully with them, donn't pull on them too hard or twist or kink 'em.
You could just have flakey NICs too, try swapping with one of the working units.
Good Luck
Scott