Crystall, there are a couple ways your friends can go about this- They can exchange outside of Marriott Vacation Club (MVC) for a different company's timeshare, or trade for Marriott Rewards Points (MRPs). However, the time of year they have their timeshare may not coincide with a Marriott property's rewards availability. Having MRPs gives your friends flexibility to stay in other properties outside of MVC, but there are restrictions- availability being first and foremost. The exhange rate for MVC to MRP may not be as favorable as one may wish either- with different hotel tiers or categories that have varying points values per night. However, if the hotel isn't a popular one, the further the points will go. If you don't want to stay at the same time they have their timeshare, that is another advantage. Having a full villa is one advantage of a timeshare that hotels don't offer though.
I just checked my MVC account and found out that this benefit- trading for MRPs, is somewhat different for different MVC owners. Destinations club owners have pretty much unlimited ability to trade for MRPs, with certain deadlines. For a weeks and enrolled owners it says
You're eligible to trade your timeshare ownership for Marriott Rewards points when:
If you purchased your timeshare ownership week through a resale with a private party, you cannot trade it for Marriott Rewards points, but you can still earn Marriott Rewards points in other ways.