It is very difficult to get lambs to take the bottle once they are a couple of weeks old, and you can't tube them any more either. They are also getting quite a challenge to catch!
So the decisiosn is probably made for you by now, keep and eye on the ewe, make sure she has got extra feed, good grass and always lots of water. Alaso remember Mg lick, otherwise grass staggers and watch out for hypocalcaemia/milk fever too. Ewe has to produce quite a lot of milk....
Other thing is to maybe have a creep feeder for the lambs?