Make sure they are not too thin, maybe keep a lick in the field and plenty of hay. Also would feed a bit of concentrate if they do look a bit think right now. They will need an increasing ration of concnetrates, but difficult to do if you don't know when they are due at all!
Did the previous owner vaccinate with Heptavac? if not, or you don't know maybe discuss with your vet about best way forward. They would be due a booster about 4 - 6 weeks before lambing, to give some immunity to the lamb via colostrum.