Thanks for the replies. Just to confirm, I do pick the horse and pony droppings up daily, so that they don't clog up the paddocks. I have had hay out for them to pick at but neither the pony or the sheep are at all interested so I'm not sure if they are hungry or not!
Condition score wise, I'd say they were between 2 and 3. They were all fed well for a good 6 weeks before lambing, twice a day, according to the feeding guidelines for twins (I didn't have them scanned so just assumed twins for all). Three out of four did have twins (we lost one at birth due to cord separation) and the other had a single so they were all fed correctly.
I think what I might do is supplement them with come coarse mix for a while and see if they improve a bit. They are all up to date with worms and fluke. If they don't improve, I'll get rid of the bigger horses and stick them on the bottom paddock instead.
We will be keeping two of the ewe lambs, probably, but the other four will be going to slaughter, perhaps around Feb/March time.