My son and daughter both have an old non-expiring park hopper ticket with 1 day remaining. Can they use this and turn their GAD to get the fastpass option? Is this a valid multi-day ticket since it only has one day left and is a few years old?
Yes. The rules just state "valid multi-day ticket". This eliminates one day tickets which may have been bought as part of a package, but there is no requirement that more than one day remain on the ticket.