I have kept lambs on a ewe with mastitis in one quarter, but i topped up three feeds a day with milk replacer.
The lambs are much more settled with mum than without her but you have to make sure they are getting enough milk or they will keep sucking her and make her life hell if she can't feed them enough then she'll get very sore and it all goes downhill from there.
Keep an eye on her and take each day as it comes if any of them start to look poorly or lambs look humped, pull them off and feed them seperately then dry up the ewe.