I'll tell you something that many people know, and you should be familiar with too. Games are good to do by yourself, but they suck if you try to do it by yourself but have no luck.
Ahh the many wonders of gamefaqs!!!
go to
http://www.gamefaqs.com/portable/gbadvance/game/12775.html
and find a FAQ that can help you.
That link will take you to many FAQS about golden sun the lost age. there is one called "Summon Tablet/Sidequest Guide"
I'm sure it will answer your questions.