Sorry we have been a while spotting your post. For some reason it only hit my "new unread posts" list today.
You don't mention the breed of your ewes, which can have a big impact on how best to feed, or not.
In general, I would not ever feed a single-bearer unless she is really thin. Lick bucket for sugar and minerals yes, concentrates no. You don't want the single lamb so huge she struggles to get it out. I would be feeding hay at this time of year, though, to appetite, even if there is a lot of grass under their feet.
Feeding twin-bearers with a condition score 3+ ... I probably wouldn't give more than the half a pound you are giving, along with the pre-lamber bucket and ad lib hay. But some combinations of ewe breed and tup breed might change that answer... for instance, a Mule ewe to a tup which produces big lambs at birth (eg Texel) might need a bit more concentrate in the last month as she simply doesn't have space for the amount of forage she would need to derive the nutrition she needs. And split the concentrate into 2 feeds. But lambs from a Cheviot tup wouldn't be so large at birth, so she can make better use of hay or haylage. And you need to be cautious feeding a Texel or a Beltex ewe or you can end up with the combination of narrow birth canal (possibly narrowed even further by internal fat with those condition scores) and over-large lambs resulting in hard lambings and even caesarians.