All three cost 1CP, which means you can realistically use two of them in the same turn.
Inspirational Battle Canticles (start of the Command phase). Target one friendly ADEPTA SORORITAS INFANTRY FLY unit or one friendly EXORCIST unit; select one friendly battle-shocked Adepta Sororitas unit within 6 inches, and it is no longer battle-shocked. A battle-shocked unit has Objective Control 0, so this is a scoring stratagem, not a morale one. It is the reason to park an Exorcist or a Seraphim squad near your objective holders.
Harmonised Exorcism (your Shooting phase, when a friendly EXORCIST unit is selected to shoot). Target that Exorcist; select one unit visible to and within 9 inches of a friendly ADEPTA SORORITAS INFANTRY FLY unit; your Exorcist's ranged attacks against it have +1 to hit. Note the geometry: the 9 inches is measured from your angels, not from the tank. Your Seraphim are forward observers. The Exorcist stays safe.
Devastating Reprise (your Shooting phase, when a friendly EXORCIST unit has shot). Target one friendly ADEPTA SORORITAS INFANTRY FLY unit; select one enemy unit excluding MONSTER and VEHICLE units that was hit by those Exorcist attacks; your FLY unit's ranged attacks against it gain [DEVASTATING WOUNDS].
The sequence is fixed and worth rehearsing: angels get within 9 inches of the target, Exorcist shoots it with +1 to hit, then the angels shoot it with devastating wounds. Two stratagems, 2CP, one dead infantry unit. The MONSTER and VEHICLE exclusion on Devastating Reprise is the limit: do not build your anti-tank plan around this chain.