How did the Yelnats family believe they were cursed, and how was the curse broken?

The
Yelnats' family curse was originally placed
on their
"no-good-dirty-rotten-pig-stealing-great-great-grandfather" by
Madame Zeroni. The
curse is a bad luck curse. The Yelnats family consistently
has bad luck and finds themselves in
the wrong place at the wrong time. This
is why Stanley winds up being blamed and punished for a
crime he did not
commit and is sent to Camp Green Lake. Madame Zeroni placed the curse on

Stanley's great-great-grandfather for failing to carry out his promise to carry her up
a
specific mountain. The curse is finally broken when Stanley saves Zero's
life (as well as his
own) and carries him up that particular mountain. The
reason that this action broke the family
curse is because Zero is Madame
Zeroni's descendant. His real name is Hector Zeroni, and chapter
50 shows
readers evidence of the curse being broken by having the Yelnats family end up
with
great wealth.