I have equally sized bumps behind both my ears. I'm wondering if they are swollen glands or just my mastoid bones?

Bones. Everyone has non-movable very hard bumps behind the ears. Swollen glands move around within the skin, over the bone. They are soft and usually smaller than 1cm in size.
Mastoid bones. They are likely your mastoid prominences. If they are equal, do not worry about it. This is normal. Good luck.