@friends-table fao media club.
In regards to kilua making a deal with his brother. I think you overlooked the fact that kilua has made several deals throughout the show.
He makes a deal with grad student guy (can't remember the name right now) to follow his rules when learning nen.
He makes a deal with the melty faced man to give him wins in the arena.
He makes a deal with his dad to come back if he betrays his friends.
I get the feeling that the zoldics probably made many such deals with kilua throughout his childhood and training. It's more effective to make someone choose to do something they don't want.
Rather than forcing kilua to stay home his father creates a situation in which he believes naturally as a consequence of his upbringing he will return to the zoldics without fail.
Also assassin's make contracts to kill people.
Anyway that's my essay. Thanks for the show.