Praise be to Allah.
It would be a great deed, If you can allow Muslims slaughter lamp according to Islamic Laws. If you can not, the only thing you can do is to sell them the lambs so they could take care of the matter on their own.
However, I urge you to try to ease matters as much as possible for Muslims so they could slaughter the lamps at your farm, for they may not be able to find as suitable of a place as your farm.
May Allaah guide us and you to all the good deeds.