Our group of 6 did this double climb as an overnight, camping at Phelps Basin.
We camped at the TH on Friday night (almost 60 cars already).
Dumbell is more fun to scramble. Steep but solid. Greenwood is more loose, but not as steep. Below the solid rock, there is plenty scree. From Dumbell to Greenwood, there's a very narrow ledge with steep drop.
Road is bad. Trail is dusty. Flowers are blooming. View is outstanding.