You need to get tough here. So what if your older DS doesn't much like you for it.
You have other priorities. Your health is important..who will look after your younger DS if you get sick?
Did you younger DS hear his older brother say he didn't want mental health issues like him and you?
You're being a bit gullible here. Gullibility combined with his selfishness means someone could well die. Think of all the people he'd be mixing with and all of the people they would be mixing with.
You cannot control your DS's behaviour but you can control yours and the reactions you have to him.
He either does Find My Phone or he doesn't get back in after he goes out.
If he goes out for longer than 20 minutes he doesn't get back in.
Tell him you won't be enabling his risky, selfish and illegal behavior. Then the ball is in his court.
If he does break your trust then he has to know his stuff will be on the doorstep. And whatever you do, stick to it.
You owe it to your younger DS, yourself and the rest of society.