Whilst he has every right to see his children, I would certainly be using his Coke habit, as a reason for him to have limited contact with them or supervised only access.
I wouldn't wave a person who takes drugs around my children and the fact that the person in question is their father, makes it worse.
He can decide whether he wants to take drugs or see his children, but he would be subject to regular drug tests before I allowed it visitation. It does not matter that he's only on drugs at the weekends.
I would stop taking calls from his family members as well.
Respond telling them you're busy and to send you a text message. That way you have evidence of what they say and I recommend doing the same with your DH.
Try and focus on you and your DC and push him aside if you can for a little bit.
It looks like he's taken advantage of your good nature for too long. He's used your condition to reduce your self esteem, instead of being supportive like a good husband would.
Take it day by day and most of all, believe in yourself.
Because you don't deserve the awful treatment he's dished out.