I have some similar questions although I'm wondering more about concentrates. My Shetlands currently have adlib hay, some grazing (the grass doesn't look enough to graze to me, but sometimes they graze even when they have hay, so it must be), a mineral block, and a red licky bucket, which they are using, but not obsessively (20 sheep, 1 bucket, about 1/3 gone since December). It's just coming up to six weeks before lambing and I'm going back and forth in my mind about starting concentrates or just continuing with the hay and maybe starting concentrates after lambing.
My mentor, who is terrific, would definitely give them concentrates, but he learned on commercial sheep and is also the sort of person who always wants to give animals more treats, he's a lovely big softy and his sheep are all fat
Mine are currently condition score around 2.5, some 3, except for one skinny ewe who I'm hesitant to supplement at this stage because she was similarly skinny last year (when I bought her as part of a group) and then had a very large lamb, so I'm concerned she'd just give it all to her babies and then struggle at lambing. She seems healthy and happy otherwise, no scour, good appetite, bright eyes.
I didn't scan so don't know who is carrying and who is carrying twins, although I have some guesses from belly size at this stage!
I'm leaning toward not giving concentrates before lambing and then see after that, but it would be very helpful to get any advice people can offer. Ideally I'd like small lambs that get born easily to ewes that have plenty of milk and nice fleeces, since I'm breeding more for wool with meat as a happy side effect, so am not fussed about market weights.