Doubt their invitation or seating has anything to do with Jack. Do we even know if jack has ever met the Clooneys before George sold Casamigos? It was reported in the days leading up to the wedding that the Duchess and Mrs. Clooney has struck up a personal friendship. Not sure about Mrs. Clooney doing any work with Prince Harry though?
There’s definitely a connection between Jack and George, which likely predates any relationship between Amal and Meghan.
https://pagesix.com/2018/05/22/george-clooney-served-shots-of-his-tequila-at-the-royal-wedding/