Is it possible to have carotid end-arterectomies on both sides at the same time?

Risky. That is a very risky strategy, and i wouldn't recommend it or do it on any of my patients.
No. Risk of reperfusion bleeding into the brain. Can do each side individually about 2-4 weeks apart. For severe bilateral stenosis, i treat my patients with carotid stents with distal protection, using this approach.