pressedcat
First Post
Let them do it if they want to. I'd say fighter takes half damage, each cleric takes 1/4 dam (initially). So if fighter took 20, it would get distributed like this:1st: The 2 clerics cast Shield Other on eachother. This effectively pools their HP.
2nd: Each cleric uses a scroll to cast Shield Other on the Fighter.
3rd: Each cleric uses a scroll to cast Shield Other on the Rogue.
........Fighter
..........10hp
Cleric A......Cleric B
..5hp............5hp
..2hp............2hp
..1hp............1hp
..___............___
..8hp............8hp
So party (fighter) gets hit for 20hp damage, they end up taking a total of 36hp damage; theyv'e really outsmarted you there

If you are going to allow stacking of the spell (which probably isn't legal), make sure they implement it properly. They'll soon work out that Cleric B shield other-> Cleric A shield other-> Fighter
works better since this way there's no feedback effect (incidentally with 20 dam as before, Fighter takes 10, Cleric A 5, Cleric B 5).