My (31M) husband (29M) and our daughter's mother (31F) decided to overrule my decision and gifted our daughter a book set I don't approve. How do I go about this without it ending up in a three-way fight?

I know our situation is a bit unusual.

My daughter's mother and I had a one nightstand when we were both 18 which resulted in our daughter who is now 13. A year later I had met my now husband and my daughter's mother had also met her now husband. Luckily for us we all get along and all co-parent together.

I should mention that my husband and her are two peas in a pod. They became best friends and while it's a blessing most of the time, in discussions like this it's a pain in the ass.

They're both avid readers of Thriller/Fantasy/Romantasy/Dark Romance etc and they bond over it. My husband occasionally ropes me into buddy reading a series with them and about a year ago, all three of us read ACOTAR by Sarah J. Maas. They loved it, I found it disgusting. Not a big deal, to each their own until our daughter who had picked up on reading from them asked to read it. I told her immediately no. Not only does it have explicit sexual scenes, it also has topics I don't want her exposed to at such a young age.

They didn't go against me in front of her (she asked over blended family lunch) but they had made their displeasure clear in private saying it's just a fantasy series, it would be healthy for her to be exposed to books like that so she has a healthy outlook on sex, it would be healthy for her to read about a strong independent FMC, etc. They were quite literally like twins pinging off of each other. One says something and the other builds up on that and vice versa.

I stood firm with a hell no. Regardless of my views, facts are facts. The series has slavery, entrapment, sexual assault and physical assault not just by the 'villain' but by the MMC who is supposed to be morally grey, explicit sexual scenes that are disturbing with the highlight of the MMC reaching his peak to an image of his child, racial discrimination about a magical species, classism etc.

They said that I'm reading too much into it, it's just a series, it's supposed to be just fun and I agree. I usually don't care about the books my husband asks me to read with him but this series was so blatant that it was disgusting, and I don't want my impressionable young daughter to be reading it. Not to mention the series rating is 16+.

They weren't happy but her husband had also backed me up since we had discussed the series before so imagine my goddamn surprise when my daughter came back from her mother's yesterday and hugged me and thanked me for letting her read the series with my husband looking guilty behind her.

I didn't react and still haven't reacted if I'm honest. Sometimes my husband gets carried away and I can tell that's what happened here but I'm still pissed. As far as I know she's barely started the first book which is the most tame of the series so that's something and is going to be reading it at her mom's using her copies. I know I can't dictate what happens when she's there but I also can't back down on this. How do I go about this?