The bottom figure does indeed to be wearing the garb of a Roman legionnaire, and I wonder if that is not intended to be Constantine. The problem, though is that the figure under the horse looks moorish to me, which would be anachronistic.
Here is a statue of Constantine:
The top figure appears to be Christ.
The second row could be a bishop on the left, and a Christian King on the right (Charlemagne?)
Perhaps the expert, Technical Editor, could tell of its’ authenticity?
Charlemagne is who I first thought of as well, for that figure on the middle right.