I'm not seeing what hints to a fourth person, myself.
Gloved hand wrapped around his penis. It isn't his hand or the brown-eyed girl's. We can't see the red-eyed girl's left arm but there's no way she can reach far enough to fondle him from that angle.
Gloved hand wrapped around his penis. It isn't his hand or the brown-eyed girl's. We can't see the red-eyed girl's left arm but there's no way she can reach far enough to fondle him from that angle.
But the hand is oriented such that it could only be coming from under Browneye, so it must belong to Redeye. The proportions are just junk as expected.