Sean Hampton's comfort toward William Bishop and refusal to believe the cross would repel vampires makes sense when you take into account he's already friends with Old Bridget and the Skal community.
Sean Hampton going crazy and murdering everyone in his district seems out of character given other Skals' behavior who aren't psychopaths. Then you realize he's infected with the blood of hate. This also explains why turning him into an Ekon will cure him; feeding him Jonathan's blood exposes him to the same immunity to the Blood of Hate that Jonathan seems to have.
Lord Redgrave only banishes you from the Ascalon Club when you defy him despite Elisabeth's claim he will try to kill you. Later, when you return to the club for William Marshal's blood, he folds like a cheap suit no matter how hostile you are. Then you note he sends Ekon assassins after you, who try to kill you. This is because Lord Redgrave is of a lesser lineage and you've already killed his chief enforcer. Redgrave is a Dirty Coward!
Lord Redgrave is only able to get away with passing himself off as William Marshall's progeny due to the fact the Great Hunt destroyed most of the ancient vampires in England. As such, no one is there to contradict his claim but Elizabeth.
Lord Redgrave's misogyny and distrust for immortal women probably comes from the fact his wife, Old Brigit, loathes him for changing then abandoning her.
Lady Elisabeth has no desire to change her daughter Charlotte because she's infected with the Blood of Hate and would create another monster. Ironically, now that she knows Reid, she could probably have him turn her. We also discover that the change is very often lethal.
The existence of the Blood of Hate explains why the vast majority of vampires created during The Spanish Flu seem to be a collection of psychopaths. The influence of the Red Queen has made them into monsters with a Horror Hunger far stronger than Jonathan's own. Regular Ekons and Skals may be good or evil but the ones created by the Disaster are Always Chaotic Evil.
Jonathan doesn't seem afflicted by the Blood of Hate, despite regularly feeding on Skals. Then again, he was sired by Myrddin himself, a vampire so powerful and ancient his species is unknown, which likely makes him immune to the effects of the Blood of Hate. That probably also explains why, even as a newly-born vampire, he's able to take apart much, much older and seemingly more powerful and experienced vampires. This would also explain why Jonathan turning Sean into an Ekon could cure him of the Blood of Hate, since he's just one step removed from Myrddin himself now.
Within the game, it is possible to turn three different characters into vampires by choice within the story, via specific in-game options; Geoffrey Mc Mullum, Aloysius Dawson, and Edgar Swansea, but these have variable costs to your XP. Jonathan notes himself that there is no guarantee that the transformation will work, but perhaps it has something to do with the general health of the body. Mc Mullum is still in the prime of his life and has just drunken the blood of King Arthur (himself a vampire), so even though Reid has just fought him, is still young and healthy and perhaps even more physically able to endure the transformation, hence why turning him only costs 1000 XP. Dawson costs 2000 XP, as he is literally dying, but this is due to old age, and he has physically and mentally prepared himself for the change. Swansea costs 3000 XP, but has been beaten severely, and is suffering various internal injuries, which will soon kill him by the time you find him.
None of Reid's coworkers ever seem to comment on his looks, despite the fact that he looks like a walking corpse. Then you realize that dr. Reid works the night shift. When they see him, they just assume he's tired from working all night.
It's shown that it's possible to turn someone into a vampire by accident by just biting them as seen with Mary Reid without having to exchange any blood. It's inevitable that you gonna have to chomp on a few enemies to regenerate health and gain experience points - especially when playing as an Friendly Neighborhood Vampire, since this is the only way you can level up. Let's hope that Jonathan makes sure his victims stay dead and don't rise as vampires...
Assuming that Jonathan being unable to gain experience from draining Prywen guards isn't Gameplay and Story Segregation, Mary must have drained a ton of civilians to catch up to him as quickly as she did.
Which may add a layer of understanding as to why, if Jonathan hasn't killed anybody, she chooses to let their mother go, but still tries to fight him to the death; not just rage over having been murdered in the first place, but perhaps as a form of Suicide by Cop. Jonathan, after all, has proven resistant, past that first overwhelming urge to feed that resulted in Mary's death. Mary isn't made of the same stuff, and recognizes that she won't be able to control herself the way Jonathan can.
West End has a sizeable population of Ekons (and two Skals right behind Jonathan's house). Jonathan's mother Emelynn has a tendency to wander off alone due to her schizophrenia. It doesn't take much to realize that she is in constant mortal danger with how much of an easy picking she is.
As a matter of fact, if you kill Avery the butler unless you kill her yourself first there will be no one to watch out for Emelynn and she will wander off and get turned into a Skal.