Unfortunately I missed a change in some variables within webtrees which broke this component a coupla versions back.
The latest v1.3.1 fixes this and is now back to a single Joomla login.
My gripe isn't with the program. My dissappointment is that there is absolutely no way to contact the developer. You can look thru the installation documention and FAQs on the website, but if that doesn't work, you are out of luck!
There are links to a forum, but the links are broken. There is no Contact Us link. It would be nice to see someone take ownership of this really nice extention!