Adult son in a mess. What to do

Before I start what could be a long post I'm guessing I know the answer but would benefit from your collective wisdom and sense check

My son is 26. I adopted him with my ex husband and then my current husband. My husband has 2 children both grown up and moved out. Our son has been difficult growing up. He was diagnosed with ADHD without the H and has always been disorganised and didn't fare well at school. He has had several jobs some for weeks with a couple for years but does just about enough and I suspect does not name a great employee. Last year he met a girl and despite neither having any money or any intention of being together she became pregnant with twins. Sadly the twins were born sleeping at the turn of this year at 28 weeks. Since then we have also lost my ex husband, his mum my uncle all of whom my son cared about. He can be manipulative and abusive verbally and it got to the point my husband was saying to me it's him or me. We found a 1 bed flat locally for him to move to with bills paid that he could afford. He moved in in July. We agreed to pay 6 months rent to get him set up. He had a car loan a bank loan and a store card. Since then it is as if he has lost the plot completely. He has taken out payday loans, not paid any of his car loan or Bank loan or store cards and has been let go from his job. He has nothing to show for anything borrowed. He is not taking drugs but it is likely he treats his friends to days out etc as he seems to buy friendship. He said losing his job was because of being on probation and having time off to go to hospitals with the twins but there must have been other things as I'm sure that wouldn't be legal.

Where do I go. I've always helped him when he's been out of work by sending in his cv. This time he didn't admit to losing his jo. For over a month. He lied about being in work all that time whilst borrowing money from universal credit . I've contacted his doctor as although he is an adult I was hoping with a bit of background He could check In his well-being ( he is very overweight and never seems happy)

I should just leave him to it. I suspect he needs to hit absolute rock bottom before he makes any change however what fears me the most us his birth father hit rock bottom and stayed there.

I can't afford to sort his finances and I don't like the way he is with me or my husband. The rest of the family ignore him. I am a bit fearful of him too. Whilst he has never been physically aggressive he's never been this far into a corner.

I've paid off a couple of the massive interest rate payday loans and will pay his phone and probably car ins and tax for this month in the hope he can get another job quickly. Plus a couple of speeding fines too. A lot of this borrowing is against our address. I have made him contact Step Change but he has not acted on their advice.

I have to stop now don't I. I'm really really sad. I see our other children doing well and settled and this situation is breaking me. Thanks for listening.