Altering payment options

I had a 6-month account that was due for renewal in about a week. I tried to cancel and had some issues that have been resolved, but now that still leaves a question in my mind.

From what I understand you have to cancel a long term subscription and re-subscribe at the shorter interval. What happens when you have a staggered 2-key account with lots of chars? My account is up next week, the wife's is in about a month. Let's say next week I have not re-upped at all, will one of us still be able to log in since there is still one active sub on my account?

I plan on renewing both subs, but if for some reason I only renewed one, how would my account react to having more than 5 chars with only one sub? Does it matter?