How to set the camera zoom to include always two objects

Im trying to get the camera to follow 2 player objects.

step one was position a thrid object between the two. People on here helped with that.

The next step is the camera. How do I set the camera width to always enclude the two player objects, whether they are close together or far apart. Maybe something like 'include both [or distance of both] plus 100 pixels on each side.