I'm with Ferdinand on the issue of trusting Gervasio. Sure, he was not the one who came up with and ordered the massacre of the Ahrensbach nobles, but neither did he appear to try to stop it, or even mind it too much, beyond considering it distasteful. As the king of Lanzenave, he surely would have had the authority to order Leonzio to desist, regardless of the political factions and even if Leonzio hadn't listened, he is much stronger. I suppose it is possible he learned of it only after the fact, but I doubt it.
Also when Raublut talked about killing those who oppose him, right in front of him in the auditorium, he just started to belt out blessings, without a single word against the killing or any attempt to negotiate a somewhat peaceful settlement.