Hi CS and welcome to our online family,
You have a very full plate. I am so sorry to hear of the tragedies that have befallen your family in recent years. I hope you are seeking help and support for yourself beyond resources like this forum, although this forum has been a lifesaver for me and many others, it is not enough. You will also need support in real life whether that is from family and friends, counseling, communities of faith, self-help groups such as Al-Anon and CODA or anything else available that works for you.
As far as your children are concerned, it's complicated even more by the fact that one son is already a legal adult, and the other is close behind. This changes your rights, but it also changes your responsibility from a legal perspective (the "mom" responsibility doesn't change though and I understand that).
The first thing I would suggest is to as they say, put your own oxygen mask on first. You will need to get to a place where, emotionally, you are able to detach from the decisions of your (misguided, mentally ill, but still adult) children enough to protect yourself from the insanity they create. Al-Anon has been a terrific resource for me in this regard and I recommend it highly, as has its cousin Codependents Anonymous also known as CODA.
Many of us mistakenly believe that we can somehow fix our broken children. We cannot, and many of us will sadly bankrupt ourselves, drive ourselves insane, or even literally die from the stress of trying to control our kids' behavior. We have more (legitimate) resources at our disposal if our kids are minors but even then, once they reach adolescence our influence is frankly minimal. Many times it comes down to our own willingness to let our kids experience the consequences of their choices even if it brings them peril. It is extraordinarily hard and many of us cannot ever get there. You will hear from other parents here in time who faced the same decision and are facing it each day. You will hear their stories of what they did and how it worked out for them and their adult children.
As strange as it sounds, taking the focus off what they are doing and focusing instead on your own needs and boundaries will eventually bring you to to the answers you are seeking. For example, you will need to decide if you are willing to keep your sons under your roof in whatever condition they are in, just for your own peace of mind that they are sheltered and have access to food. That is a very personal and difficult choice, and nobody will judge you regardless of the choice you make.
There are ways to evict your adult children from your home. You should check with the laws in your state to ensure you follow proper procedures. Some states require a formal eviction procedure to be followed.
You may be able to petition the court to step in with your 17 year old. They may be able to send him to a facility - jail, rehab, group home - where he can get help for his issues. But remember - you will never be able to make another human being do what you want them to do. If your son doesn't want to take his medications you can't make him. If he wants to smoke weed, you can't stop him. You CAN prevent him from doing those things under your roof, you CAN refuse to pay his bills if he refuses to work, and you CAN refuse to bail him out of jail when his mental illness and drug use inevitable cause him legal problems. But that is again a very personal decision.
Hope this is helpful. Stick around.