From reading medieval texts of that period, especially in France, killing the civilian population, women and children included, after a surrender, would be a rare occurrence and if it happened would be absolutely looked down upon. You say it would be ludicrous for someone to care about innocent lives, you understand one of the tenants of knighthood was about protecting those who can’t protect themselves, right? Not to mention, the dynamic between the Church (the many Archibishops of cities, the Pope) and the temporal powers of the time. They would have been convicted of Heresy for those crimes.