Bismihi ta'ala

As far as you are concerned, following the madhhab of Ahlul Bayt (a.s.) is a part of your personality and identity, and your marriage should not obstruct your affiliation to your Shi'i identity. This should be made clear to your fiance. 

In regards to your future children, you as their mother must try to nurture them in such a way where they are aware of their religion and abide to the laws of Islam. Which madhhab they choose is completely up to them, when they become mature and of age. 

If you instill within them the love of religion and the urge to pursue truth and evidence, and allow them to research and read and decide themselves, you've done your obligation.  The rest is for them to decide. 

Your main focus must be on accompanying your husband to be in a noble spiritual way, and avoiding anything that would hurt or harm his understanding of Islam, or your understanding of Islam. 

Be the parents that you should be, and that would be the best thing you can do.

With prayers for your success.