Mine get to scoops of pellets a day and round barrels of hay kept out in the pasture for them.
You might buy feed and hay then and ask your BIL to give them some morning and night - wait until you get there and take a look at what he is talking about.
Maybe he said that it would be more than they could eat, and that his boss sells hay for you to have the option of deciding whether to bale the hay and sell it to his boss?