I would never give powdered colostrum if the ewe has milk. It's not hard to milk the ewe for a feed for the lamb - even if you only give it 150ml of her colostrum, it makes a huge difference. But if #1 lambie has drunk her dry and #2 lambie isn't full, and it's 2am, then I'd give milk saved from another ewe if I had it. Next best, a good powdered colostrum, one that has probiotics. I find that much better than cow colostrum for the very first feed.
I agree the comment about it being the best first feed colostrum while it's yellow. Some ewes produce that for 24 hours or even longer, some only for a couple of litres then it's gone.
Milk from a ewe that lambed within the last 24 hours is best, but there are probably still good antibodies for another day or two. If I only had Day 2 ewes' milk, I'd probably do half and half powdered and ewes' for that first feed.
Any lamb that doesn't get ewes' colostrum or reconstituted colostrum the first 6 hours is very high risk for not making it. It may not die straight away but it is very likely to fail at some point in the first few months. Yoghurt will probably help it get started, I agree, but I wouldn't expect it to make a fat lamb or a breeder unless it got actual ewes' colostrum or a good reconstituted ewes' colostrum. Vaccinating at the earliest opportunity (I think it's three weeks for Heptavac for a lamb suckling a ewe, but do check) would probably help its chances.