I notice you've not answered the question - How do you know about this, OP?
Have you actually seen the Will for yourself, or is it just something one of your parents may have told you during an argument?
If it's anything but the former, I wouldn't necessarily believe it. My MIL frequently told my DH, that she was going to disinherit him, because she didn't like me, but over the years things changed, she got to know and love me, and ended up leaving everything between her 2 kids.
With regard to your own situation, I have another couple of questions:
How old are your children now?
AND
How much time do you currently spend with your parents, and does your DH make any effort toward them at all, ie, does he visit with you, offer to do little repairs or tasks to help them, etc?
I personally am in a situation similar to your parents, and know that if my child's partner could get their hands on the inheritance my child should get, the money would be wasted. I have therefore decided, much as I hate having to do it, to leave my estate to my grandchildren, but will also leave instructions with them, that they see to it that my child is never left without a roof over their head, which is what is likely to happen if they stay with their current partner. It breaks my heart to know that this will hurt my child, but I simply couldn't bare it, if everything I've worked for over the years, were to end up in the hands of their partner, as I know they would do a happy dance on my grave, if they thought they were going to get their hands on it.
I haven't, and won't be telling anyone my plans, and so will be leaving my child a letter explaining my reasoning, and will just have to hope they will understand, and be glad that, (assuming my whole estate doesn't end up paying for my care), their children will benefit, even if they can't, due to the bad choices they themselves have made.
However, should my child make the decision to get rid of this partner at any point up to my death, I will immediately make plans to change the Will in their favour.
So, maybe, in spite of what you believe about your parents and their beliefs, you might be surprised OP. I'd therefore recommend, as other posters have done, that you go ahead, and divorce this man who isn't making you happy, get on with your life, and plan on supporting yourself. Then if anything should change with your parent's Wills, it will come as a nice surprise.