Sorry in advance for the long post.

My son's last year of high school his Dad and I took him to the ER because he had told some friends that he was suicidal. After speaking to the crisis counselor he agreed to be hospitalized. He was already 18 so it was his decision. He was diagnosed as having bipolar 2. They started medication (I don't remember the name). He stayed for 10 days. He stopped taking his meds less than a month after he came home. He has never tried medication since (3 years ago) and refuses to believe his diagnosis. 
He has been unable to hold down a job. He's down to 130 lbs at 5" 9'. He doesn't eat much or sleep much. His room is full of trash, dirty dishes and dirty clothes. I help him clean it up about once per month when it gets truly disgusting. He stays to himself most of the time. He's extremely angry and hateful sometimes. Sometimes he breaks things in his room. He's punched holes in his bedroom wall. 
His sibling came out as trans over a year ago. He is very transphobic. They basically hate each other and rarely interact. Sibling said she will go no contact after she moves out. I don't blame her. 
He went through a break up a year ago and which made things worse for a long time. He started talking to me about his feelings. He won't open up to anyone else. Things started to seem better. He agreed to therapy. I was hopeful but it only lasted a couple of months. He had an episode a couple of months ago where he was breaking things in his room again. He said he doesn't want to live like this. 
I talked him into talking to our family Dr about his symptoms. I asked if he wanted me to leave while he spoke to Dr but he wanted me to stay. She had him complete a depression assessment on the computer. Then she had him do a bipolar assessment also on the computer. She said it sounds like he has all the symptoms of having bipolar. We spoke about medication. He didn't want to be on a mood stabilizer. She suggested a new medication, Vraylar. We filled the prescription. He refuses to take the new meds. Didn't even try them. He said he's not bipolar. He swears he just has ADHD. He was diagnosed with ADHD as a child and took Concerta. He is unmedicated for ADHD now. He said he might be ok with trying ADHD meds again. He did discuss trying ADHD meds again with the Dr. Dr told him that he can't take Concerta as he is unwilling to stop smoking pot. She said she can prescribe a different non stimulant medication instead. He said he'll only take Concerta because he thinks it helped.
Last night my daughter had her cousin over who is nonbinary. My son sends me a hate filled transphobic text expressing how much he hates the cousin. He expressed a desire to beat the cousin up. He blames the cousin for my daughter being trans. They didn't interact while cousin was here. We have discussed that fact that whatever his feelings, violence is not allowed. Neither  is verbal abuse. He knows I will kick he out if he becomes violent towards anyone. He knows he is not allowed to speak to either one of them unless he can be civil. 
I'm at my wits end here. My therapist wants me to set a deadline for him to get a job or he has to move out. I don't want to kick him out. I can't force him to take meds or go to therapy. He is following my rules about not interacting with cousin or sister if he can't be civil. At this point I don't see him ever being able to hold a job down if he refuses to get treatment. He swears pot is the only thing that helps him. He works here and there doing the occasional odd job and spends it all on pot. I'm not opposed to pot but I wish he would consider taking meds and/or going to counseling. 
This is having a devastating impact on our family. What more can I do to help him? If you have bipolar and were in denial at some point, what helped you to decide to take meds and/or get therapy? If you are a fellow family member of someone who has been diagnosed with bipolar, how do you cope?