They had to trick him into thinking that he was attending his brother's wedding when it was actually his own engagement ceremony. Leon didn't realize what was going on until he actually saw both Angie and Livia in front of the altar and started trying to come up with all sorts of excuses not to marry them. Problem is that with both Leon's and Angie's families being there in an official engagement ceremony, abandoning Angie and Olivia would've really destroyed both their reputations and humiliated Angie's father who set up the whole thing. Leon really had no choice but to get engaged to both of them or he would've dragged everyone through the mud.
Leon is too much of a coward to have done anything to anyone yet, but that doesn't stop him from collecting heroines and villainess to add to his harem. Leon also ditches his irritating no kill policy in the war, but goes right back to it when the war is over.
Zel Lespinasse is Noelle's real family name, but she goes by Noelle Beltre and considers it her real family name more than Zel Lespinasse. I personally like her bubbly personality better than Angie, but Angie is a great girl too.