Whoa Nelly!!!!!! It didn't take long reading your post to be concerned. You ask "How much are the payments?" The payments should be zero because financing isn't recommended for a luxury purchase like DVC. We waited years to save the buy in money and the wait was worth it. Even having DVC paid for the trips still aren't cheap, you have tickets, meals, airfare, etc. It is thousands of dollars a trip.
The other concerning part of your post involves buying in with a relative. This is a recipe for disaster. What hapens when the old family fued starts or you want to take an extra trip or use more points? Buy your own DVC with cash or skip it altogether. The break even tretches far longer when finance charges are factored in. Do you have at least 6 months of savings that can cover your monthly budget? Do you have retiremnet savings, investments, college funds, etc. If the answer is no to any of these you are not DVC ready.
Really think this through. Maybe I'm reading to much into your post but you don't sound like you are anywhere near the decision process.
Good luck with this.
Mary