If I have a seizure disorder, am I more likely to seize in alcohol withdrawal?

Yes. Alcohol withdrawal makes seizure more likely even in people without a pre-existing seizure disorder. If you have such a disorder, it further increases the risk. On the other hand, if you are already taking anti-seizure medication, it may make alcohol withdrawal seizure less likely. It won't protect you from other medical complications of alcohol withdrawal though, which can be serious.
Yes. Alcohol acts like a very weak anti-seizure medication, but it also burns out the receptors that seizure medications use to work on the brain.