There seems to be a problem in the scripts or I don't know... I can't look it up because I don't know how to use the CK for these kind of problems. The only thing that I can tell you to do is to set your spouse a vampire manually setrace NORDracevampire while he/she is in console target Replace NORD with your spouse's actual race. (DARKELFracevampire, HIGHELFRACEvampire, etc) Better than nothing, imo. As far as I know, even if you do the quest your spouse doesn't have a lot of new dialogue (like, 1 phrase) and you still get attacked if you transform into vamp lord. Sorry if I can't help more, I had the same problem but I let go of it because Serana is boss, even if not possible for marriage.