I agree with Crayola, I would make them ALL go down at naptime. If they don't sleep then that's ok but with consitancy after a while, I'm sure even the older ones will sleep for 30 minutes. Sometimes we think that just because a child is very active he does not need to rest when actually he is actually actind up du to a lack of sleep.
As for the other problemes, was the 4 year old use to a daycare setting ? Maybe he also needs to get use to a daycare setting ?