Sorry to hear you're frustrated, but be prepared for 18+ months. There's new administration coming, and because of this USCIS may be shifting focus to other areas.
Make sure to pay for I-131 so he'll have ability to travel overseas without abandoning Adjustment of Status. For example, his mother gets sick back home etc.
Make sure to pay for I-765, so he will get work permit. This will not only allow him to work legally while waiting for green card, but also open bank accounts, build credit history, get driver's licence etc.
Good luck!