Unless you have already got the Combinex at hand, you maybe want to investigate if they actually have worms and/or fluke.
That would be a faecal egg count, but would cost some money thorugh your vets. The reason why it would be best to test in advance, if the sheep were done before leaving their old holding and your ground was clean they may not have worms! Same for fluke, but it is a bit more difficult to see their eggs, and it would only be from the beginning of Nov they would be detected anyway. I am also not sure if they build up resistance to flukicides as much as they do for some of the wormers.
My sheep have been here for about three years now, and have so far not needed worming, but we have had fluke however, so I am on Fasinex only. I think I will drench mine soon as well.