How does Twain use coincidence to further his development of the character of Huck?

It's a coincidence that the Phelps (the people who bought Jim) are also Tom's aunt and uncle; it's also a coincidence that they're expecting Tom any day, and when Huck shows up they believe him to be Tom. The fact that Aunt Sally mistakes Huck for Tom, gives Huck the added bonus of being able to actually "play" his idol for awhile.