There is nothing wrong in your marriage from this girl as long as Alhamdullilah you follow the Sunni path and left the Ismaelite sect, and through your relations with Muslims in the mosque and its imam you can prove for them that you do not have any relation with the previous sect beliefs or principles and that it is not your fault your family is still following this sect.

As we recommend you to continue in holding good relations with your family as much as you can and try to present and set for them the best example for the Sunni Islam hoping Allah to guide them all.

In her response to your question, the prominent Muslim scholar and Da`iyah, ZeinabMostafa, states:

Alhamdullilah that Allah has guided you to the right direction and true faith in Islam. You should explain yourself very clearly and declare what you believe in order to seek credibility with the family of this girl.

A recommendation from the local imam, community leader, and the like can help in this regard. The most important thing to focus on is how you now represent yourself and not your parents’ beliefs. May Allah make it easy for you!