I want the Know your Enemy perk for maxing out relations with danse. I don't really care about him beyond getting that perk.

I'm also allied with the brotherhood, and planning to stick with them

How do i make this work. Give me all the wpoilers you want, just tell me how to get that perk, and keep my alignment with the brotherhood

Not that hard. You just need to pass some hardish persuasion checks. When you are sent to kill Danse, just talk to him and persuade him that it's worthwhile for him to live. When Maxson shows up, you must pass a difficult persuade to convince him to spare Danse.This should unlock the perk assuming you have maxed approval with Danse at that point. The Brotherhood will be hostile to you whenever he is with you so just refrain from bringing him anywhere near the Boston Airport or the Cambridge Police Station. If he kills some Brotherhood patrols out in the wildnerness somewhere it doesn't change your status with them.