Corrected for typo (mode 4, not mode 6)…..
Mode 4 will align to the edges of the people based on the select subject photoshop tool. Mode 4 doesn’t use face detection. You must also check the checkbox to “use Select Subject” before starting the batch. If you don’t check that then it will align to the transparency edges which for non-cutouts will be the edge of the frame.
Other than mode 4, there is no other way. The face detection is not set up for multiple people and as you found out will select 1 face at random.