For me the old days were long before big brother. I've been doing this a long, long time.
spoiler alert for anyone who hasn't played big brother
From the backstory, we know that the mother, Ann and her sister were abducted and raped when they were younger.
The story begins much later when she is older and has 3 children living at home, the Father of these three is absent.
I theorized that when Ann was abducted and held captive, she got pregnant. But because she was so young, she put the baby up for adoption. Enter Eric, successful businessman, pays to track down his birth-mother. This makes Eric the "big brother" titular character, and Max is little bro. Mind you, Eric's Father was a serial rapist kidnapper, but he doesn't know that, because he was adopted off, and there was no record of the Father, Eric only got info on his mother and looked her up. Initially Eric wants to meet Ann after all these years. Imagine his surprise to find that Ann has 3 children, that she kept, while she had tossed him aside. She's his flesh and blood mother, and he has feelings for her, but there's some resentment against Ann for adopting him off, and even more resentment against his half-siblings that she kept. They didn't have to go through what he had living in the foster system. Needless to say Eric has some issues that need sorting out.
Eric sees that Ann is in trouble, needs money to pay bills, etc. It's his mother, and he's in a position where he can give her a job. It's a perfect way to meet Ann, without being all awkward "hi, i'm the son you didn't keep" just give her a job, and get to know her first, then tell her. Well, that didn't exactly go as planned. Ann, being hot-blooded, single, and not knowing that Eric is her son, sees Eric as an eligible bachelor, wealthy, successful, generous, kind, handsome, and has a nice tan. Plus he has a car, no more having to take the bus, or order groceries online, and get melted ice cream in the mail, so gross. Cougar Ann wants a piece of that man-meat. It's a little conflicting, being his mother and all, but she's hot, and maybe she deserves to be punished for throwing him away when he was a baby.