Hi,
What ages and weights are they?
How often are you offering - because you seem to have tried a heck of a lot of things in only a month.
Offering food too often can actually decrease the chances of them eating - especially if you routine keeps changing from what they were used to.
Are you handling any of them?
How certain are you that nothing has changed in their setup - are you using thermostats or dimmers for example?
dr del