There’s clearly an error here and your parents need to resolve it or they risk being treated as overstayers if they don’t leave by 1st October.
They can take their passports to the nearest CBP point of entry or Deferred Inspection site and get the records corrected. I would expect that a reasonable officer would extend the passport date beyond 7th October, but there is a possibility that they’ll stick to the 1st October date and update the online records to match.
Find a Port of Entry
List of Deferred Inspection sites
Credit:stackoverflow.com‘