@hanna21,
If you choose this marriage and convert, your parents will disown the children? Is this correct?
If so, you're forced into making a choice that means creation of a permanent rift with the parents - the people who brought you onto this earth. You have a horrible choice and there's a tug-of-war for your soul that is an unfair position in which you've been put.
The choice is your's, his and theirs. There is no right or wrong. It's up to you, your future husband and your parents. However, the answer has the potential to destroy any chance of future happiness if there's marriage with this man.