While their names are never said, there's a naming scheme behind them. The grandfather's name is Ichirou which means "first son". His son is named Jirou (second son). The two grandsons are named Zaburou (third son) and Shirou (fourth son). The grandmother is named Mako. Jirou's wife is named Mami and their daughter is named Mari.
Actor Trivia
Ichirou, the grandfather, is played by Guts Ishimatsu, a former boxer. When Raiga fights him, they get in a boxing match.
Jirou is played by Takahashi Takuro who was the Garigari popsicle monster from Gouraigan.
Sano Miku, who plays the female victim, was the bride in Yami wo Terasu Mono.