Your son-in-law has two options:
1) Apply for Palace Chase, he will transfer his enlistment commitment over to the Air National Guard but that will require him to double his time left with the guard, i.e. a 4 year contract with 2 years served would require a 4 year deal with the guard unit picking him up. The Air Force is looking to let go around 44k people in the next coming years, so this is a viable option.
2) Apply for a service commitment waiver. What this means is your son-in-law can file the appropriate forms and walk away from the government owing them nothing. He keeps his bonus (if he got one) and his GI Bill. This is a better option because once you walk away you’re a civilian and then can apply to any guard unit. Also, if he decided to join the guard, he wouldn’t have to double his contract or attend basic training again.

Both of those options are going to require the Commanders signature on the forms with their approval/disapproval stamp. Even if the Commander says no, he or she doesn’t have the final word on if you get out or not. Randolph AFB and the career field manager make that call.

The guard unit in ID might not have any openings, so it wouldn’t hurt to apply for both.
Have you son-in-law stop by the MPF and see the Air National Guard in service recruiter. He could apply for Palace Front (active duty to reserve status) but the Reserves won’t pay tuition assistance, just the GI Bill. If he goes guard he can get both the GI Bill and state funded TA, it’s a sweet deal.

If you have any more questions, let me know and I'll give you my e-mail address so I can walk you through the process. GOOD LUCK