Calculate Roll, Pitch, Yaw from Reference Point

I know there are a number of questions on here regarding Euler vectors and roll, pitch, and yaw. This is more of a mathematical question than a Matlab implementation.

I have a set of positions given in ECEF coordinates. I also have a reference point that is "looking" at those positions. My question is, given this data, how can I calculated the roll/pitch/yaw of the aircraft? Do I even have sufficient data to do so? If not, what else do I need?

I've read the Wikipedia page on Euler angles, and while helpful in a general sense, I am not sure how to apply it here. All approaches I have seen tell you how to calculate the Euler vectors given the Euler angles, but I need to know how to get those angles.

If someone could tell me "you need to use Approach X" that would be very helpful. I can then look around on here and see which Matlab implementations I can use.