A Mother's Love - the entire concept of this game is based on MC having an affair with his girlfriend's mother and this game already has "abandoned" tag and was "on hold" for a long time but according to information available from dev patreon he is currently working on the next update of the game.
Off the Record - unfortunately game is abandoned.
Love, Lust, and Rock 'n Roll - 2dcg game, here MC can cheat on his girlfriend either with her sister and also her mother.
Being a DIK - if MC "dating" Sage and also fuck one of his teacher Jade who is Sage mother then I think this also matches what you are looking for.
Defending Lydia Collier - if you choose Ellie path then you can also fuck her sister and mother.
Kelly's Family: Mother in Law - game completed, as title of the game suggests MC may be having an affair with his future mother-in-law.
Become a Rock Star - game completed, if MC choose Selina path then she becomes his girlfriend and he can also cheat on her with her mother.
Back to Freedom - game use real porn, MC have a wife and can also fuck his mother-in-law.
