According to Official Guinness Records,
The most family members to complete a marathon (multiple generations) is 30 and was achieved by the Hughes Family (Ireland) at the Dublin Marathon in Dublin, Ireland, on 27 October 2014.All of the runners are descendants of Padraig and Marie Hughes. The fastest runner was Hillary Hughes, who crossed the finish line with a time of 3:34:28.
For a complete list of 2014 records, please visit 2014 Guinness Records in Ireland.