Thank you for this information. I suggest that you are not going to be able to rationalize with the daughter. And, of course, the Mother can bring you into her home and leave with you.
You can try to contact the local sheriff in the county and request an escort because you might be expecting trouble. They may or may not go with you until there is trouble, unfortunately.
And if they do not go with you, then I suggest you go to the home, you get your Mother in Law to a local attorney and have her complete a Power of Attorney for you and your husband which means that you and he will be in charge should the MIL not be able to make decisions.
I suggest, too that you can talk to the local attorney about having the daughter and her husband evicted. This is a process and not one that you will want to take on yourselves because of the temperament you describe for the daughter.
In the meantime, I suggest that the only way your MIL will be able to do anything before you get there is to call the police, tell them she is afraid of the daughter and she is abusive and request a restraining order until eviction can be done
My concern with that is the daughter may say the MIL is crazy and request she be taken in to hospital for 72 hour evaluation.