I'm also nursing 2 year old twins. My twin boys are about the same age as yours (they'll be three in October).
They nurse anywhere from once a day to three to four times a day. With my boys, if one's nursing the other HAS to nurse. And then it's smack down- they'll wrestle with each other, slap me, grab each other. To be honest, it can be a little exhausting nursing them and I'm hoping that they'll wean soon..