What a terrible situation you find yourself in… my heart goes out to you at this worrying and anxious time.
I don't know if it's what you're looking for, but there's quite a lot of information about genetics and MS on this page:
And there's lots more to look at by following the links at the side of the page.
I think it would be helpful if you could get yourself referred to a geneticist, who might be able to make things clear for you – you're in a complex situation that is probably outside the remit of a family doctor – but don't be surprised if they ask to test and monitor your whole family over time because I am sure they will see your dreadful situation as an opportunity to gain valuable, and possibly unique, information.
I hope that talking to an expert will ease your fears a bit,