tyria to shining jea

if you start you character in tyria, can you bring them to the shining jea islan, where you start out with new factions characters? and if you can, can you get the 2 15 attribute quests?

Yes, you can get to the island with Tyrian Characters. Just head to the Marketplace from Kaineng and then go talk to the guy on the docks.

I don't believe you can do the 15 point quests in Cantha with a Tyrian Character. But I do know you can only do one set of quests or the other.

Yes you can go to Shing Jea, but you can't do anything there. No quests, just 2 missions that you can do for the title or exploring.

And you can't do attribute quests in Cantha with a Tyrian char and vice versa.

only 1 attribute quest allowed for each character

You can only do ONE quest there and the missions (with no reward) - the attribute point quests are chapter specific so you can't do those with your char.