focus on b12 for testing, you want the level at least 500 pmol/L.
you can address the whole b-complex via a good high quality b-50 complex. if you want to do a short term therapeutic thing you can take 2 b-50s 4x/d for a week (so total 400 of each per day), then switch to 1 b50 a day. for b12, methylcobalamin is the best supplemental form. if you find a b complex that uses that form, great. if not, buy that one separately for use in the shorter term. don't take more than b-100 per day in the long term. you will be getting some from food and at intakes over 100mg/d i nthe long term, vit b6 can cause peripheral neuropathy. also you can google search term klenner4 to get a specific list of b vitamins to use for ms and why. but you can ballpark the approach with oral b-100 complex.
of course food sources are best so hunt them down via sites like www.whfoods.com