Thanks for all the answers.
Just to be 100% sure; So it doesn't matter if I move the spous of a non-immortal in before or after marriage?
I didn't know about this. So generation 7 is the only exception to what you are saying here?
You won't be breaking the rules by moving in the spouse of a mortal, but it's not the best strategy. Space in the house becomes critical by the 3rd or 4th generation and having extra Sims in the house that aren't required for the challenge could backfire on you. For example, if the mortal marries and has twins, you've got three spots in the house taken up by unnecessary Sims. Then, say, one of them live an unusually long life. You could end up with no space when you need to bring in an heir.
As for the issue of having both parents living in the house when the heir is conceived and born, this is from the rules on page one:
"Immortals must result from natural pregnancies of Sims living in the Dynasty house."