My advise would be, get a feacal egg coutdone!! A bit of poo from each lamb, fresh, as they drop it, put in individual bags and ask your get to do a feacal egg count. Then when you are given the result IF they need wormigthevet can advise and give you the necessary amount for your lambs. The will need o know the weight of the heaviest .
The spray for keeping low fly off is another matter, speak to theve, if he's helpful, eve if they don't have some you would buy they maybe able to put you in touch with another small producer who would share. Alternatively someone on her may be able to help.