I absolutely echo the "don't feed" advice.
If you're worried about supplementation, you can give them minerals and vitamins by drench, so you know they've had it. And put out treacle or a treacle lick, or sprinkle treacle or molasses on their hay, so they can get the sugars they need in the last 6 weeks.
Depending on when you lamb, would you have time to help a local farmer with his / her lambing? You'd learn loads, and having helped out there would never feel awkward or embarrassed asking them for help with your sheep.

If you were to have similar problems again, you could for another year consider using a smaller breed tup for your shearlings. A lot of Beltex and Texel farmers hereabouts use a Shetland on their first-timers, and say they rarely if ever have to assist. Also the lively little lambs know what to do even if the mother doesn't, so there are less post-natal complications too.
We used a Shetland on two commercial Charollais X hoggs last year, as an experiment, and were very happy with the outcome. We would certainly use a Shetland again if we were tupping hoggs. (Generally we don't tup hoggs here.) And we're using one of the tup lambs from that liaison to tup a few of the smaller shearlings this time, hoping for slightly smaller lambs but that will nonetheless grow on well. Oh, and nice fleeces too
