cat sitting

my dear niece recently moved to the area with her two adult male cats - Chunk and Spike. They are very large. Spike is a tuxedo cat and Chunk is a wild boy with long dark fuzzy hair and big blue eyes. She is going out of town for Thanksgiving and is leaving her two fellows at my house. I have Monster Kay and Oat. Oat and Spike have similar temperments and Chunk and Kay have similar temperments. They have never met.

I would like to introduce them using the best methods available. So far I figure I would separate the groups for the first day and then introduce them one on one. Then what?

I can send the ladies out in the backyard if things get testy and kay spends most of her days outside sunning on the deck but these fellows are inside cats. Oat sits on the sofa and blinks. or at least I think she does.

any advice on introducing cats to cats