We don't know that Sookie undid Eric's influence or if he overcame it himself.  All we know is that she restored his memories.

Also, we only know that two humans can be glamoured at the same time.  We don't know exactly how many more can be.  

Does anyone know how long the trance lasts?  I've seen it last a little while, like with Russel and Jason, but I'm fairly sure it can't last forever.