Give him art time after supper when it is just him and your daughter which leaves you free to tend to her. Since your son is the oldest can you adjust naptime so after lunch the others start their naps and he has a half hour craft time which tends to be a relaxing time anyways and then lays down for his rest. Or if he goes down with the others does he wake early and can do a craft till the others are awake. The purpose of one of those play yards is to keep the baby and the older child apart since they want to do different activities. Since there are so many younger children you might want to consider some sort of play yard that will allow you to gate off an area that only your older child can go into. If you used shelves to form the walls and then one of the walk through gates you could teach him how to open it to let himself in and out.