Correcting some misinformation:
The only significant disadvantage of buying resale from other than Marriott is that you cannot exchange the use of your week for Marriott Rewards points.
Thus, among other things, a resale purchaser has the same right to make reservations 13 months in advance as those who purchase from Marriott. If you look at the CC&Rs for your resort, the FAQs at the MVCI site or the FAQs for this Marriott forum (at the top of the list of topics for this forum), you'll notice no 13-month restriction related to resale buyers.
I'm not sure you can use the 13-month reservation system, if one of the two weeks is a fixed week. My recommendation is that you call Marriott and ask and then post your response here for all to benefit from.
For a moment, I'll assume you can use the 13-month system. As ciscogizmo1 states, to use the 13-month system, the weeks reserved must be consecutive or concurrent. Thus, for example, if the Streamside fixed week is week #14, your call to Marriott to reserve your Maui week would have to be for week 13, 14 or 15. If you wish to reserve any other Maui week, you could call only 12 months ahead.