MSM (methylsulfonylmethane) has been hyped as a cure for arthritis, based on a lot of testimonials but very little valid scientific data. MSM also claims to help constipation, allergies, and even to stop snoring. MSM has not been shown to preserve cartilage, nor halt joint destruction and deformity. That alone tells me all that I need to know about the benefits of this drug.
With reference to how to deal with you Mother, perhaps you can politely tell your mother and your brother that they are free to try any new regimen that they feel will work for them. However, according to your research and what you know about your body and your Lupus, you choose to stay with your current regimen and you do not want to do anything to risk a flare-up of your disease, or to risk causing a fatal event by not taking those medications that you know are saving your life. You could tell them that you have the utmost respect for them and their decisions, you ask only that they give you that same respect. If and when the time comes when you might consider changing your regimen, you will be certain to come to them first for information and/or advice. But until that happens, would they please respect your decisions just as you respect theirs.
I am sorry that this is causing you so much stress. I hope that you are able to find a way to make them understand so that you can alleviate that stress, at least. Wishing you the very best.
Peace and Blessings
Look For The Good and Praise It!