Bipolar can skip generations. So even though all 3 of your children have bipolar, it does not imply that you and/or your husband have bipolar.

HOWEVER, it is technically possible that you and/or your husband have undiagnosed bipolar. I'm obviously not a dr, but if you are concerned, then definitely see a doctor!

Have you looked at your extended family to see if there are any kinds of mood disorders there?

As for it being "normal" for all kids in a family to have bipolar... Well, I cannot say. My sister does not have bipolar. The only disorders we have in common are anxiety stuff.