Just to be different, if you don't know when the others are due, I'd let them all out so they can get some grass. (I know that will depend on how easy they are to catch again if you need to though).
If the weather is good, we don't even bring ewes in once they've lambed, but instead build a hurdle pen around the ewe to allow bonding and to prevent anybody else from stealing the lambs. Just a thought....