At 17 you brother is in real danger and the clock is ticking down to his 18th birthday. Your dad will not be able to force him to get help after 18. I truly believe with such little time you need to call the police and force a psych evaluation, NOW. He has shown that he's an immediate danger of others School doesn't matter that's the least of his concerns right now. If he is in a treatment place he will be attending therapeutic school. He can get just his GED and attend college just the same but right now that is not important.

If you are near mercy they have inpatient child
take him to Alexian Brothers