How to Calibrate more than 2 cameras?

[aviralchharia]

Hi, I was trying 3D human pose estimation using $3$ cameras: i.e., first finding 2D keypoints from each of the $3$ camera frames and triangulating to get the 3D pose. In such a case, how to get the camera extrinsic parameters? Specifically, for $3$ cameras, should we use $[C1, C2]$, $[C2, C3]$ pairs or should we use $[C1, C2]$, $[C1, C3]$ to find the extrinsic matrix of the cameras?