jacobsos is right in just about everything.

However, the ANG does allow your son-in-law to use Montgomery GI Bill benefits. In addition, some states will pay full tuition to in-state colleges/universities if he decides to become an officer. But that's more likely in the ARNG (Army National Guard) than the ANG. That also depends upon each state. State tuition benefits usually do not cover flight training.

I used Montgomery GI Bill benefits (Chpt. 106) in 1993-1994 to obtain instrument and multi-engine instructor certificates. It does work.

If he wants to use those benefits at a military flying club, he might want to stay in the vicinity of an installation which has such a club. The military club prices are noticeably lower than non-military flight schools. I suspect there's no military flying club in Boise, Idaho. I used one at Quantico MCAS and was a member of the Army National Guard when I joined.

Good luck!