If you've good grass and the ewes have plenty of condition on them, and you want them to try to rear all three, then I'd give the ewes cake - 18%, a good feed every day.
If, as they grow and demand more, the lambs seem hungry, just take one off, full stop. It'll take to the bottle when it's the only game in town!
If the lambs seem other than replete, don't leave them on to 'see how they do' - next thing will be ewe with mastitis, and you're bottle-feeding all three (that's if you don't lose one, or them all. And maybe the ewe's udder, and/or her, too.)