Not long ago, there were a fair number of charitable organizations that accepted timeshare donations. What they did was turn around and sell the timeshares to generate funds for their charitable purposes. However, most of those organizations found it quite difficult to resell those timeshares and stopped accepting timeshare donations.
There are still a few charities that accept such donations, but only if they believe they will be able to sell the timeshare and make a profit after incurring the expenses associated with the transfer and sale.
Bottom line: If you can't sell your timeshare in today's dismal resale market, it's extremely unlikely you will find a charity that thinks it can do what you can't.