If you have no control over requirements and a bunch of people who can't work together towards a common goal, I'm not sure what, if any, methodology will work.
The main complaints against Agile by developers are:
1) I want to hide in my technology rathole and never come out.
2) I'm allergic to accountability and can't take people asking me once per day what I'm up to.
3) I don't want to have to talk to other people.
So, if any of those apply to someone you're going to implement Agile with, they're not going to be happy.
Agile is as much a cultural agreement as a methodological agreement.
The main complaints against Agile by developers are: 1) I want to hide in my technology rathole and never come out. 2) I'm allergic to accountability and can't take people asking me once per day what I'm up to. 3) I don't want to have to talk to other people.
So, if any of those apply to someone you're going to implement Agile with, they're not going to be happy.
Agile is as much a cultural agreement as a methodological agreement.