Yes, you can combine as many certs as you want per meal.

And no, they can’t be used for breakfast, only for lunch or dinner, IME. I am sure someone will be along to say they have been able to in the past but I have tried at three different properties over the past couple of years, most recently at the Fairmont YVR in April, and, was told no all three times. Not sure about afternoon tea. Maybe call and ask?