I doubt that Malcolm knew everything, however I don't think he was totally ignorant about Margaret's world either. However we still don't know what Malcolm
was told so he would go along with it. Then again, Margaret could have told Malcolm everything, but how much would he be able to understand or believe? You would think that Margaret would have run into the same problems that Harry did trying to explain his world to Susan and even Murphy.
Yeah. The more I think about, the more significant it gets. Morally, if Margaret really was trying to 'go straight', she had an
obligation to make sure Malcolm understood what he was buying. He's getting a lot more than a sexy wife, after all.
Stop and think about it from Malcolm's POV: the biggest issue isn't necessarily Margaret being a Witch, though that's no small thing. There's also the fact that she's a
century old. OK, maybe Malcolm was attracted to older women. But along with that, comes her own past crimes. Would you be casual about marrying a murderer? Or whatever else she had done?
Plus there's the fact that he's quite literally
risking his life from her foes by getting entangled with Margaret.
Margaret was being hunted by the bad guys
and the good guys. The (more or less) good guys wanted to disconnect her head from her shoulders, Lord Raith and who knows who else probably wanted to do substantially worse. A mortal caught in the line of fire is not safe. The Wardens probably would go out of their way to avoid harming Malcolm in getting at Margaret
if they could. But if they couldn't...
The White Court and who knows who else was after her would at best be indifferent to Malcolm's survival, many would eat him or take pleasure in killing him along with getting her.
The more I think about the implications of the Margaret/Malcolm marriage, the more complicated and impressive they get.