I'm sure you don't want to do this, but where I live - in Texas - you can arrange a court order to the VA's psychiatric hospital. No one will be happy, but if it keeps him alive or keeps him from a serious injury to himself or another . . . .I believe you would start by seeing a social worker at the VA hospital or by going to a civilian Judge in the county/district. Best wishes and blessings to both of you in this challenging time. As you can see from the many responses to your post, you are not alone - you have us.
billie And PS: your son should qualify for both VA and possibly SSDI disability benefits.