My heifer had twins is that common?

Nope. It's more common in cows to have twins (on occasion) than in heifers.

Often heifers do not have enough milk to suckle one big calf, let alone twins, so watch how the calves are behaving when they finish suckling her to see if they're still hungry. If they are still hungry, you may have to bottle feed them in addition to the heifer suckling them.