Beets too big for quality?
Just because beets grow big does not mean they can't be good to eat, if mine ever grew that big I'd celebrate! One beet can feed your entire family at that size.

Try roasting one of them until you can stick a prong into it easily, then remove it and let it cool. The skin will just pull off, they you can cut it and try it. If it tastes like a beet should then treat it like any beet. If it is a bit bland then you can still use them, you just may need to add extra flavors.