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

Did you mean in chapter 32?

Did you mean specific to chapter 32?

yes .

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.