To be honest with you, he would be better forgetting about the dumbells entirely, as they are not going to be much good to him.
He would be better to do something like the following, 3-4 times per week.
Jog/steady run - 2 miles.
Bear Crawls - 5 x 20m
sprints - 5 x 100m
Plank - 3 x max time
That should take him 45 - 60 mins, and will do more for his endurance and overall strength that mucking about doing 200 arm curls with a pair of biscuits