Can Family Reunion be used...

to get you back onto maple island if your junior/senior is there?

Well, you'd have to originally be on Maple Island with your junior/senior, since you have to be in the same map in order to family someone.

Even then, probably not, since KMS probably noticed this loophole.

Family reunion works for any family member I believe, not just the one directly below you. Have char 1 be a Jr. for char 2 on Maple Island. Make char 2 leave Maple Island and be a Jr. for your main (let's say char 3). Family Reunion to char 1.

tested already, cant be used cause family tele act as tele rock bought on cash shop, both blocked to go on maple island

cant go to pqs event maps and boss maps,and maple island

Yup, can't be done. Though, I don't know much about the supposed "Maple Island Return System" that I've heard about, so I'm leaving a nub there just in case the future changes things.

You can't use it to get inside the girl's sauna either :[

If I am not mistaken, on JMS, I think you can return to Maple Island when you get over a certain amount of fame. I can't be bothered to hop on and check right now... so I'll wait for some JMS players to comfirm that...