Stacking Quests?

Does anyone know if you can stack the old quests with the new ones? Or do they have to be achieved separately? Can you even have two in the same deck?

You can have two in the same deck but only one can be active at a time.

So probably not worth doing.

Thanks, I've been looking for an answer for this for an hour or so, much appreciated. Specifically the warlock quests have awesome wild overlap but if you have to do them separately, not so much.