For Flashpoint... can you "share" the victim POI marker?
Yes.

You can consider the cost in dealing with victims having to do with moving them, not so much carrying and holding onto them.  So if one firefighter moves a victim to square, there is no cost for picking up or dropping the victim, simply a cost to transfer the victim from one location to another.  With this in mind, you can walk up to a square where a firefighter has just moved a victim and continue to move that victim into a different square, assuming you still have enough action points to bear the load.