German HW pickle: 'meine' vs 'meiner familie'

[Teets]

Y7 vocab/phrase test revision. Chapter heading = "Meine Familie".
But the first phrase to learn is: "Es gibt...Personen in meiner Familie." DD stressed about whether that extra 'r' is a typo or not after being traumatised by Twinkl worksheets errors at primary. Any kindly German speakers around?

The -r is correct. It’s because ‘in’ is followed by the dative form.

German DH says the r is correct

Oh, you lot are the best. Thank you. DD has autism and this one detail is causing mayhem for her. So kind of you to put us out of our misery so fast. Thank you! (I did try Googling it but got thoroughly confused).

She'll also come across it in the genitive case, just as a heads up! Das Haus meiner Familie =my family's house 🏡

Thanks so much, sleepymama3!