I would say the two older ones are old enough to take responsibility to feed and play with the dog. The two younger ones, I would supervise the interaction for awhile until you really get to know your new dog. Since it's only been a week I think there is a good possibility it will all work out when everyone gets to know each other better. Watch the dog's reactions to different people and it will help you get to know how your dog thinks about certain actions, etc.
Snake Vom Eselspfad RN CGC (AKA Raina) 3/5/08
Pyrate CGC 4/1/03-5/16/12 RIP
Too many to list waiting at the bridge but remembering them all