Spectacular, but there is a mistake: their slashes come from the same side (from viewer's eyes, left for Vader, right for grandpa), as i infer from their hands grip. So this block is impossible. Moreover, they look quite still, you should add more dynamics to their poses.
It's not impossible. Vader is holding the way he is, and Obi Wan seeing an opportunity, swung at it, therefore making Vader's saber go toward the right. Now that it would take a moment to switch his hand positioning and swing back at Obi Wan, Obi Wan can slash again... Or so I speculate.
Moreover, they look quite still, you should add more dynamics to their poses.