Books with title Tournament Trouble

Monsters under the bed and mermen in the fishtank are normal around the Gates' house. The Gates are the keepers of the portals of the worlds. Many adventures lie beyond the gates. With the intruder in the Gates' world, a minotaur on the loose, and people missing from a tournament between the worlds, what else could go wrong? Unfortunately, it could get worse, and Ed must step up or someone will die.