We never used to kiss both cheeks - just the one - but it is becoming more commonplace now. Certainly I'll greet people I know well by kissing both sides. Men don't kiss each other at all, by the way.
I think it will depend on when your story is set. Marauder era then stick to one kiss. If you're moving into 90's and your characters are in their 20's then they can kiss both cheeks.
Older people (in their 60s and above) will only kiss on one side.
Hope this helps.