[Lava]

The variables decide are used to identify state of quests and talks. As I said, I don't know any reason why no talk trigger when you click him. Check the variables in near infinity. You may also use console to force someone to join, but that does not set any variables so it could get even messier. 

As for the purpose - nope, it's just for items and for taking breaks. Storing companions there may cause huge story / NPC problems. Check the other thread for more details. 

And here's more info about the console: 
https://gibberlings3.github.io/iesdp/app...a/bgee.htm