If all the kids in my family get seizures when they run a fever, does that mean my baby will have seizures?

Yes. Febrile seizures do run in families, but i don't think that means your baby will definitely be prone to these. I recommend you read about these and learn 1st aid for seizures, just in case. Keep in mind that though they can be scary febrile seizures do not cause any damage.
No. Febrile seizures, or seizures that occur with fevers, are inherited. However, there is less than a 50:50 probability with each pregnancy that they will be inherited in that particular child. Even if you already have 6 children with febrile seizures, that does not automatically mean that the 7th child will also have them.
Possibly. Febrile seizures occur in families. You do not indicate whether you or your spouse have had febrile seizures. While there is a risk for your child, there are steps to take to lessen the risk. Speak to your pediatrician. At the first indication of illness, begin fever control. Your doctor will give detailed directions.