Gift certificates are the same as cash. I wouldn't see why you shouldn't be able to.
Not sure. You would have to ask.. I only went once
Given that they're supposed to be the same as cash, I'm sure it's fine. The only issue is usually with coupons and discounts, but a gift certificate isn't inherently discounted.
Not sure if when you say gift certificate you mean gift card. I don't see any issues using more than one gift card but if it is some kind of certificate there might be some restrictions but they should be listed on it.
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