Fire Red/Leaf Green are compatible with Colosseum.

You need the Mystery Ticket to get to Island 8 and catch Lugia and Ho-oh, and you need the Aurora Ticket to get to Island 9 and catch Deoxys. These tickets are not in the games, so as of right now, without a cheating device, you can't get to these islands. However, it is possible that Nintendo will have promotions in the future that will make the Mystery Ticket and the Aurora Ticket available, like the Eon TIcket for Ruby/Sapphire.