Thanks everyone for replies
We bought some rings and applicator, which we will do tomorrow or friday I think.
Is it normal for one lamb to be much smaller than the other? Little Nancy is noticeably smaller than Norman, and he seems to be feeding more and for longer than her. Norman is quite big and solid whereas Nancy is quite bone-y and delicate.
Obviously with NY now we can't go anywhere, but should we be supplementing her food at all? Even bottle feeding her alongside mothers milk to help her a bit?