How many Keyfobs can one car accept?

It is true that every time you program one, you must re-program all the key fobs, because the one(s) you do not program will no longer work. This is to keep someone from being able to add a key fob to your vehicle without your knowledge. Here is an article that walks you through how to program them step-by- step: http://www.shareyourrepair.com/2014/09/how-to-program- keyless-entry-remote-for-2004-2010-toyota-sienna.html