before i started for the republic i did oh my papa and right now i have him packing up the camp and i went to colonel and asked for an alliance but i dont know how to ally them. i can assassinate him and il do that but how do i do it without being noticed? thanks!

Steal his key when he's sitting at the table, then at night sneak into his room and shoot him in the head with a silenced 10 mm. That's what I did anyway, worked perfectly.

I ended up getting the Great Khans to leave the Mojave altogether by completing the quests of convincing the people who he takes counsel from to go against Caesar. Then I just got his second in command to say something stupid in front of him and then told him that he should stand as his own nation of great people and to go carve out their own legacy. And they up and left, and it worked for me!

Just make sure you have a high Speech!