If I decide to set up personalisation I understand I can arrange it so if my wife unlocks the car with her key the seats move to her location - and if I unlock it with mine they move to mine.

What happens if we each approach the car (as we do) each carrying our keys - (as we do!)? Does it throw a wobbler? 

 

How does the personalisation interact with the seat memory built into the seat? Do each override the other in some way?

It will be fine. When you get to it, even if the seat is in the "wrong" position  the car will give you a drop-down menu of available profiles. Choose the one you want and it will ask if you want to move everything. Hold down the right scroll wheel and the seat, mirrors etc will move to your profile position. It's an excellent function.