The Affidavit of Support is potentially enforceable for life. It expires once:
your parents die,
your uncle, aunt, and all their children die,
they all naturalize (become US citizens), or
they all get deported.
But keep in mind, the Affidavit of Support is only a promise to pay the US government back should any of those people become a financial burden on the American people. If they live normal lives, don't apply for public assistance, etc., it's a non-issue.
An immigrant from Europe, I live on the American Riviera and work as an attorney in Santa Barbara, California.