As others have asked - what resort, what unit size, what week do you own?
You Inlaws gave this unit to you ten years ago, and one would assume they were doing so to be kind, not to saddle you with a worthless week. To me, that indicates that maybe they knew how to use their ownership, and you never bothered to ask them to show you the ropes.
Unless it's a studio unit in a run-down resort, I find it hard to believe that you can't exchange a week in St Martin for anything worthwhile. What are your expectations? Are you looking only for summer and holiday weeks? (They are higher demand because everybody wants them). Are you looking for a 3BR unit because you want to take the kids? If you have 2 or 3 (or even 4) kids, you can fit in a 2 BR timeshare easily. It will still be bigger than 2 hotel rooms, and you'll have kitchen facilities.
To get a better exchange, you need to commit to exchanging and start looking for what you want a year ahead of time. No, you can't call in mid-January and expect to trade into a top location during your kid's spring break. Those weeks are already taken.
You say you have tried to exchange, but where have you done this? If you've only tried direct exchanges through TUG or other places, that's not going to work - direct exchange requires more flexibility, because you have to accept a week from someone who wants YOUR week. However, when you use and exchange company, you don't worry about who will use your week - the exchange company in effect creates a chain of many owners using each other's weeks. But you do need to request early, and don't expect them to have what you want right away - but if that can find what you want if you give them time.
As for that flexibility, it is sometimes a good thing. You can't use the timeshare like you would a vacation in a hotel - you don't call up and simply reserve your room. If you can pick a window of 2 or 3 weeks when you can vacation, call and find out what is available. Pick something in driving distance, that you might not have done if you were reserving a hotel. You might find yourself surprised. The money's already spent, so for the cost of an exchange fee, and gas to get you there, you'll get a week away with the kids. Maybe you'll find a resort you really enjoy, or maybe you just get some quality time with the kids.
Your Inlaws gave you the timeshare for a reason, but probably didn't realize you wouldn't know what to do with it. They probably already understand the benefits of using it. Perhaps you should ask them to help you. Yes, it means admitting to them that you've never used their gift. But they can probably "hold you hands" through the process the first couple of times until you understand how to best use what you own.
