How many hay racks?

I think one hay rack should be fine if you are feeding quality hay and it is unlimited. How big is the hay rack? Can both get to it at the same time and eat?

Yes, they can both eat the hay at the same time. It's large, as wide as a grid and a little over half the height. I fill it in the morning and top it off in the evening, it's never completely empty. I just got Sweet Meadow delivered today, so we'll see how fast that goes (as opposed to Oxbow).

One should be fine. I have two hay racks for four pigs but I could probably get away with just one if I wanted to.

Two should be fine. I have 3 different sections of 8 square feet in my cage. I have a hay rack in each section.