Aidka
Like most I have no issue with the emperor not being killed, as long as both the pitiful sons suffer greatly and Clause either fully corrupts the empress to abandon her two **** sons or dies upon realizing her treachery to her two sons sleeping with her enemy. I definitely favor the grandfather's help over the church.
only logical choice really, gain an ally instead of a powerful enmay where there is no shortage of them. trade off ur father doesnt die, but will sufer for 50 more years. all wins around, would actully be moranic to make another choice, specially that his father is a small fry in the larger scheme of things to him at least. if he was a hero thats still making his way up the power structure u can find a reason for him to refuse, but still would be dumb even then. but justfiable.