Finiky cats (3) wont eat Costco's Kirkland cat food anymore. What can I do?

Kirkland food is crap. Take a look at the ingredients label. It is nutritionally akin to sawdust. There is a reason your cats are not eating it, they know it has no nutritional value. Most foods like that use a meat flavored oil to make it more palatable. Purina is a common brand, more stores than just Target carry it, including grocery stores.