en_tn/dan/07/26.md

the court will be in session

This means that the judge will be ready to investigate evidence and make his judgment. Alternate translation: "the judge will judge" or "The judge will sit down"

they will take his royal power away

"the members of the court will take the royal power away from the newest king"

royal power

This, here, refers to "authority." See how you translated this in Daniel 7:14.

to be consumed and destroyed at the end

This can be stated in active form. Alternate translation: "and consume and destroy it in the end" or "and completely destroy his royal power in the end" (See: rc://en/ta/man/translate/figs-activepassive)