Get Your Dog Care Questions Answered by Experts
There are some links to food triggered seizures..but the chances you would have two dogs doing this is not likely. I would do some research into the environment...the water, lead toxicity, etc.
If all else fails you just might be the owner of two idiopathic seizure dogs...not common, but possible.
Let me know if you want to discuss further...but I do think you need to schedule an appointment with your vet so he/she can do some research in environmental triggered seizures.