Hi and welcome,
To be honest your post information confused me, if you are a non identical twin (fraternal) it's not a mistake if people do recognise you as twins because you are still twins, just not the identical kind...
Unlike identical twins sets, genetically you and your twin will be the same as any other first siblings. Fraternal is from two fertilised eggs and not the one egg splitting into two embryo's and producing identical twins. Basically, being a fraternal twin or brother/sister sibling doesn't statistically make much of a difference when it comes to neurological conditions like MS.
It's actually much more common to be the only person in a family diagnosed with MS, than to be from a family of multiple MSers, it can happen but as Alex pointed out its rare.
Hope that helps..........JJ
It depends if you have other people in the family with MS. There are families that have MS but statistically it is low.
Alex