Answer by taking a quote from the following article:

Born in Drouin to Alfred and Colleen Ablett, Gary Ablett grew up in the Latrobe Valley in Victoria's Gippsland region alongside his four elder brothers and three sisters. Ablett displayed a love for sport at an early age, winning the state school high jump at 10 years of age. He was also awarded both club and competition best and fairest awards for Drouin at the under-11s, under-12s and under-14s levels. After citing waning interest in school, Ablett dropped out of high school at the age of 15 years to become a bricklayer's labourer.

Two of Ablett's brothers played in the Victorian Football League - Kevin Ablett, who played for Hawthorn, Richmond and Geelong, and Geoff Ablett, who played for Hawthorn, Richmond and St Kilda.  Ablett's eldest son, Gary Ablett Jr., has followed in his footsteps to play for Geelong. In 2007 and 2009, Ablett Jr. won the Cats' best and fairest award, emulating a feat established by his father in his first season with the Cats back in 1984; he also won the Brownlow Medal in 2009 and 2013. Another son, Nathan, was drafted in 2004 (48th pick) by Geelong under the father-son rule. Nathan initially refused to play AFL Football because of his father's experience with the media, but, with encouragement from the club, was signed ahead of the 2005 AFL Season and has since established himself in the full forward role Gary Snr made his own. On 29 September 2007, both Gary Jr. and Nathan contributed to Geelong winning its first flag in 44 years, capturing the premiership that proved elusive to Gary Snr in his 12 years at the club. Nathan retired suddenly before the 2008 season, but he and his brother Gary Jr. were members of the Gold Coast Football Club's inaugural team for the 2011 season.  In addition to his sons, Ablett has a nephew, Luke Ablett, who played for the Sydney Swans and won a premiership with them in 2005. Two other nephews, from his sister's marriage to Hawthorn legend Michael Tuck, also played in the AFL - Richmond's Shane Tuck and Travis Tuck, who played for Hawthorn.

Was that the only ones to play football from his family?
Another son, Nathan, was drafted in 2004 (48th pick) by Geelong under the father-son rule.