Oyako x Shuffle! ~Natsuyasumi, W Oyako no Icha Icha Houimou~ (jap) by TinkerBell - Adult Sex Game

The protagonist, Hirosawa Yuuya, started living alone for university entrance. Last year, he didn't return home even once due to the busyness of his new life. However, he decided to return at the request of his sister, Hirosawa Miu, who asked him to be her tutor.
Upon returning home, his mother, Hirosawa Ayano, who had always been overly affectionate, became even more so due to the long-awaited reunion with her son. In addition, his aunt, Aoyama Reika, who is in the middle of a quarrel with her husband and returning home, and her daughter, Aoyama Rio, greet him.
His mother's affectionate pampering, his sister's proactive approach, his mischievous aunt, and his aunt's daughter who admires her big brother.
Under one roof with such four people, a lovey-dovey, naughty, and shuffled harem life was about to begin with 'mother x sister', 'sister x cousin', 'aunt x mother', and 'aunt x cousin'.