Simple question seem to have gone amis, have you grass left for them? If no you won't do yourself any favors keeping them on.
Perhaps over sow some red clover to increase growth next year.
For worming, lambs get panacure when the ewes get shorn, a hefty dose will do no harm if you don't have a weigh crate or a good eye for it. Fluke, well your address sounds like Wales so is think yes, do you have ground that becomes wet easily? If so fasinex quarterly, again don't scrimp, up here we have to double the dose as we have some resistance. Yes it has withdrawal period but at that size they are not going straight into the FC, so just declare it at the sale.