Are the grills charcoal? What all do we need to bring to use them?

Yes. Bring charcoal and some aluminum foil to cover the grates

Grills are charcoal.

The grills are charcoal, so bring charcoal, starter and grill utensils. Bring some aluminum foil too. You can reserve the pavilions on the parks website. If you use the pit grills you're going to need a lot of charcoal but you'll be able to grill for a lot of people too.