Stan Rule, an estate planning attorney in Canada, writes a very timely post about including your vacation properties as part of your estate planning. The laws he writes about are Canadian laws so be careful when reading his post.
His analysis on holding title in joint tenancy pretty much applies in California and his point about whether all of your children would enjoy the property is something else to consider. If only one child will use your timeshare, consider gifting that timeshare to that child instead of making the kids fight over it or convert it to cash so they can share the proceeds.
Be sure to consult with your estate planning attorney regarding your vacation properties no matter where in the world they are located. They need to be included in your estate plan.