The Hextalls have been mentioned, but I always thought they were special in the sense that THREE generations in a row were all high-impact players at the NHL level.
Bryan Hextall led the NHL in goals twice and points once. From mid-1939 to mid-1943 he was the top goal-scorer in the NHL. He was a member of the 1940 Rangers' team that won the Stanley Cup.
He had a son, Bryan (the 2nd), who was an NHLer, but a fairly undistinguished one. However, his other son, Dennis Hextall, was a good player despite being a late bloomer, and had back-to-back 82 point seasons for the North Stars in '73 and '74, leading the club in scoring both years. (Another 74 point season a year after those.)
And, as most here will know, Bryan Hextall (the 2nd)'s son --- and Dennis's nephew --- was goaltender Ron Hextall, who was 1st-team All Star and won the Vezina and Conn Smythe as a rookie in 1986-87.
Just impressive that the talent went pretty strongly through three generations.