As a former resident of FL, I am aware of "Baker Acts" since I am a healthcare professional. My concern is how a 15 yo that has been Baker Acted at least 6 times is in the general population. A family member has to, aside from MD's, be the one to sign for the evals: mother or father. This kid is, literally, a time bomb. Who knows if he will fatally injure his mother with a butcher knife? He's done it before(threatened her).
You need to be out of the house until the kid is in rehab; it's too dangerous. Your wife needs counseling for enabling him. Ex needs to get lost. Get restraining order on Ex for you and your wife. Stay away from the kid until he is out of the house, sounds like he will say anything.