I think Killing most of them is still too extreme I get you hate them with a passion. Only one id kill is the bald guy and id consider the rest of the leadership so they don't start an uprising over the new leadership. But id probably let the rest live as they haven't proven to me as far as I can recall needing to be dealt with like the bald guy.
Personally, I see no reason to kill ANY of them, and I hate them all with burning passion.
Trust? Wouldn't trust a single Templar ever.
Family shows best how much a Templar can be trusted. They're all either brainwashed or so stuck in their self-righteousness they can't see how utterly fucking broken their order is.
But for all their fault, and there are more than few, as much as I'd like to burn whole order to the ground, there is no reason whatsoever to kill any of them.
Cruel, evil, twisted they may be, MC is NOT executioner. He is just your everyday person (so far) whose life got turned upside down because of fucked up family valuing everything over their son.
Going on killing path is wrong, on so many levels. Spitting in someone face, or beating few up, yes, sure. Killing? Why? Just because they're cunts? Hardly reason to kill someone.
Neverwhere, Alfar and Templars deserve each others. Let them all burn for all I care.
Pardon the profanities, hard to express level of hatred I feel towards them without a few.
EDIT: That's all assuming events so far.
Should Templars/Alfar/3rd party, still interfere with MCs life once he's out, then anyone's a fair game. Out of my life, or lose a life.
(frequent setup in books: secretly OP protagonists live quiet, secluded life, until evil guys come for him, for some stupid reason...)