Hoping, I'm so sorry that his family is putting the blame on you. I suspect they are hurt and upset and feel powerless, so putting the "blame" somewhere is their way of coping.
I'm glad you are thinking about ways to do something for you...thinking about going back to school is a great idea. My daughter looked into community colleges for medical tech training...It's so much more reasonable than private schools and the programs are great. She was able to get federal grant aid...the applications were available online. Many community colleges have their degree programs and information online...even applications. Perhaps Googling ones in your area may get you started.
You are so right, you aren't the problem...you know that in your heart; we do too, and your in laws do too, I strongly suspect. I'm glad you aren't wasting your energy trying to argue the point with them...they have to find their own recovery.
Hugs and prayers.