Mark,
I think the figures under St John the Baptist are Konstantine and Helen (mother and son). The fact that she holds the Cross (she was reputed to have discovered the Holy Cross in a well) while he wears an emperor's crown (he was emperor of the Eastern Roman empite) gives credence to this also. In any case they are man-woman, not two female figures.

I agree about St Demetrius. Lyaios was a gladiator, so he probably holds dome unusual gladiatorial weapon.