Don't you wish you could just smack some sense into some people!!
There are some that just can not admit, understand, and deal with the ugly realities. Sometimes it's not all about money.
Part of his resistance is his inability to accept what is happening to his Mom. If she would just act better it would all be ok. The reality is that she has a brain disease and it is not going to be better. It is only going to be worse. His mistreatment of her is only going to make it worse for Mom, you, and for him as well. He can't wish this away. He needs to hike up his big boy pants and accept what is going on. But you already know that.
Something you said is a little concerning. You mentioned that he was using her money to get by. If he does apply for medicaid, and it appears he will have to in order to afford the care she will need, they want to see where every penny of her money has done for the last 5 years. Any monies not used for her or her care will have to be returned. Depending on how much money he has used he may be able to prove that it was used for her care but that is going to take a lawyer and detailed records. She will be required to spend her money down to a thousand dollars and then her income will be used for her care along with the supplement from Medicare. It will take away what he "gets by" on... if he can prove that all he spent was for her care.
Please continue to stand up for yourself and your MIL. Continue to try to educate him about the disease she has. Keep telling him that she has dementia... brain damage. Explain to him that if she had a broken leg that he would not be insisting that she walk. She has a broken mind and is incapable of doing better. If she has other children please let them know what is going on. If the situation become worse, then left the department of aging or social services know of the situation and ask them to investigate. He should not be allowed to verbally abuse her (or you). And if that abuse turns physical in any way... call the police! These are hard choices but what needs to be done for MIL's safety and for yours
Hang in there and keep typing....