Are there grills available for grilling out? If so, do they have to be reserved, are there many available? If not, can you bring a grill in to the swim center? Is it possible to bring umbrellas in as well?

Yes there are grills. They are under the pavilion they have there. Not sure if you have to reserve it or not. You can always call the number and ask them, but I do know they are there and you can bring umbrellas for sure. I've seen people bring canopies

You do not have to reserve. Unless you are having a party. You might want to make sure it isn't reserved for the day you want to use it.