Re: thankyou.
James, I know you're in a really difficult situation and this isn't really the appropriate forum to be giving advice but just a few things...
Diet is most important so I would stop all sweets and chocolates though I know this is probably nigh impossible in a care home.
Get an adult care social worker to assess your mums situation and whether shes receiving appropriate care (obviously not!), change care homes or move her back home.
You can certainly ask to get your mums B12 levels checked on the NHS, this is a routine blood test. If they are low, she could get injections. There is plenty of evidence to link low b12 with MS.
These links are useful...
http://www.drmyhill.co.uk/article.cfm?id=184
http://www.thenutritionreporter.com/nutritional_influences.html
May help to convince your dad. Also I recommend "Multiple Sclerosis: A Self-help Guide" by Judy Graham, it's excellent.
Avoid glutathioine as suggested in another post, it can make some mercury toxic people a lot worse.
See if you can find some support groups on the net, for people or relatives of people with MS. You sound like you could do with some support. There must be some on yahoo.
Good luck with everything, take care
Anne