Help! Step parenting disaster

Someone help me. I’m 26 and I’m a step parent to twin 11 year olds.

They’re boy girl twins and the boy... has been getting away with skipping school this year. He tells the school to call his mom because he “doesn’t feel well” and she always picks him up no matter what.

Well, it’s December now. School started at end of August...

He’s done this roughly 10 times and you know what he does when he gets home? HE PLAYS VIDEOGAMES THE ENTIRE TIME.

Now today, I have a day off of work... which he knew... so of course, he was brought home sick to me... (he knew I’d be home and they’d say yes)... now he has been playing video games for FOUR FRIKEN HOURS. He has a “migraine” and is playing videogames? Yeah, okay.

My fiancé told me to tell him to get off and I have... but he doesn’t listen to me. He is still playing it. Fortnite to be exact. My issue is..this has happened so many times this year and I’ve talked to my fiancé about it and he always says he’s going to do something about it... but doesn’t. He asks me to discipline him... but I can’t. If he isn’t around, he doesn’t listen to me. If I took his game away, I’d be the bad guy. I feel like shit honestly. I just can’t stand how they both parent

I just am afraid because we are expecting our first baby together and if we don’t see eye to eye on parenting... I don’t know how this will work.

I’ve asked my girlfriend about it and she said “Sheesh. It’s his kid. Not your problem”. It is my problem... because I love these two and worry about them. He gets away with everything between the two of them because neither wants to be the bad guy...that being said... he is going to grow up getting everything he wants

It really, REALLY bothers me. Does anyone have any input? Has anyone experienced this? It’s so absurd.