I assume that he/they have an established relationship with a neurologist and with a Primary Care Physician. I usually see these pts after the intervention, so I am vague about the genesis. I would expect either of them to be valuable allies.
I do not know of a specific book of value to you. I did a search of amazon.com for :elder care: and came up with a lot of titles that I would consider. If you have a Barnes & Noble nearby, check with them.
I have found that every county here in rural Arkansas has a senior center and they are great resources for me. Many larger communities have mental health resources available, too. You are not the first family to confront this and I have found that the medical community is well organized to deal with it if you can find an entry point.
Much of the difficulty that I see here is the fact that MS is often accompanied by diverse dementias. These are not all from the disease, but are drug-related. That is what you can control with help from the attending physicians.
Mom's situation is dire! Stress suppresses the immune functions of the body and causes long-term changes that are not good. She needs a support group, too.
I hope that you can secure help and give her some respite.
Remember that you are not alone in this effort and that sometimes a frank discussion is all that is needed to get a pt. to agree to treatment. The worst ones that I have still don't want to be unloving and cooperate a lot more than we sometimes expect. They are people whom we love and we guard against anger/accusations when we deal with them. It is difficult, but rewarding.
G_d bless you in your efforts.