I checked Microsoft's FAQ for the Xbox live gold family pack, and browsed on here for a little while, but can't seem to find the answer to my question. My wife and I both have Xbox consoles, and I was wondering if I bought the family pack, do I have to add four different accounts right away, or if my wife and I could both use two memberships. So we would both have 24 months total. I know this is probably not the case because Microsoft probably would not allow that, but I just thought I'd ask.
The memberships in the gold pack all start on the date of purchase. You don't have to assign them all at once, but the timer is ticking as soon as you buy.
Unfortunately, the only place that they tell you this is one small line on the this page:
Note Your Gold Family Pack membership starts on date of your purchase. Your credit card is charged immediately, after any discounts are applied
If you need to add somebody after the fact, this page should help you out. Even if you only need two of the memberships, it's still a better deal than buying them full price, but the unique billing system for them might make it worth just buying two of them.