This nonsense about the Williams' sisters being so talented is overplayed. They are both talented athletically, with foot speed, agility and explosiveness (when they are in shape).
But, as far as pure tennis players, they are not even in the top 20 of all time. Neither has great, soft hands. Mechanically, they both have had SERIOUS flaws--Venus with her first and especially, second serve, both of their forehands and neither has ever had a great slice.
Martina, Chris and Steffi had far more pure "tennis" talent. Their strokes were more technically sound and they had better hands--especially Evert on her groundies, Graf on her slice and huge forehand and Martina on her serve, slice and touch.
Venus and Serena have usually played SLOPPY, error prone tennis. When they were younger, they got away with a lot of garbage tennis because they beat their opponents into the ground with their power and intimidation. That lasted but a few years. They are done. Their games have not evolved. Their mechanics are still screwy and they have not developed new shots and dimensions in their games. Very overrated "pure" tennis players. Great athletes who sometimes played very good tennis. But not great tennis players as far as consistency, fluidness, creativity, finesse, etc. Most of the time, their matches against each other were flat out awful to watch.