Try not to panic, and spend some time talking to your lawyer. It's going to be ok, you just can't cave in to him because you are afraid. I get it because I've been there.
First of all, is getting your divorce involve a trial? In many states, not. Most likely, there will be a full day at the courthouse and you will be paying your lawyer by the hour for that. Yes, expensive but necessary it sounds.
The courts in all states will look at a parent's potential earnings, so quitting a job to not pay doesn't fly. That parent is still responsible for the amount they should be able to pay (in my experience, the judge settled with an amount a little less than what it should have been, but didn't fall for the lies of being let go from his contract work).
But you said he is going to claim disability. Talk to your lawyer about this and show the texts. It's really serious to falsely claim disability, so if you think he's doing this, so if he is then by all means make noise about it. Your lawyer will have some ideas about this, most likely contacting his lawyer to let her/him know you all will be outing him on this.
You said you had homeschooled, so you must have spent much if not the majority of time taking care of the kids at home. And the current situation with weekends only sounds like their regular routine has been with you. That is what a judge will look at - what can help ensure stability and routine for the kids (especially if they have to go from homeschooling to a school setting, that's a big change). But time will need to be set for them with their father. Are you ok with most or all of their weekends with him? If so, you should be able to just continue that and no more from what you are doing right now, but if not (you and the kids do not get much relaxing down time together - what about the traditional one weeknight, every other weekend with him plan?), now is the time to get that change. It's hard to change visitation orders after they are set unless there is a big life change.
Also, ask your lawyer about visitation for the 16 year old, usually that is about the age orders don't apply because kids that age want more flexibility in choosing because of their own needs (jobs, friends) and from the sounds of it, your X is trying to control things and you will want to make things clear that the 16 yr old (who will be 17 next year) has a say in the situation.
Hang in there! You can do it because you have to. The more you can talk to your lawyer and through her/him to the judge about the reality of the situation, the more fairly it will work out and in a way that is fair to the kids and you.