How old will they be when you plan to wean them? Usually the ewes have just about weaned their lambs themselves by 4 months, certainly by 5. I would wait until they are just about weaned before sending them off, then you can do it in one go, especially if the lambs are all going together, which would reduce their stress.
From the ewes' point of view, it's usually suggested that they need 2 months dry to get back into condition for tupping.