If you want to stay somewhere besides SSR, your in-laws can call for a reservation 7 months prior to arrival. For March 2010, the 7 month windows open in August, 2009. If the in-laws have developer points and are offering those, then only SSR is an option for you.
If the points are regular SSR points, then I think you have a very good chance of getting a non-SSR March 2010 reservation at 7 months. Just ask the in-lws to call on the first day possible to have the best chance of getting your first choice. Unless you are after something very limited (like concierge at AKV or the less expensive options at AKV, BWV or BLT), you will probably get your first choice.
You could ask the in-laws to book SSR now as a back up and then call again to switch at 7 months (assuming you want to stay elsewhere. SSR is very nice). You could even waitlist at 7 months if your first choice isn't available. Up to you and it depends on how accommodating your in-laws are. Very nice of them to give you the points.