# asking as a favor

Here the word "him" refers to Festus.

# to have him transferred to Jerusalem

This can be translated in active form. Alternate translation: "that Festus might order his soldiers to bring Paul to Jerusalem"

# for they were preparing an ambush to kill him along the way

They were going to hide along the road and kill Paul as he was passing by, but Festus was not aware of this part of their plan.