After Dinner Drinks

Two magpies drinking from the birdbath late on a hot day:

Our resident magpie family has (we think) three babies this year. It is hard to be sure as there are quite a few members of the family. The bird in the rear is definitely a juvenile. The bird in front looks older, as its beak has white on it which the juvenile is lacking, but not completely adult. Is it possibly an older sister, maybe from last year? The youngster was hopefully asking it for food, but not getting any!