Huge family fight. Need advice?

I'm on nobody's side technically, but my mom is right.

Its a long story, but because my mom didn't buy my sister an IPhone 6 because the upgrade costs more than my mom expected, my sister threw a huge tantrum and there's more I don't want to get into

But my sister disowned my mom, made stuff up, CAS is involved, etc.

My sister took my mom's iPad with her, and has a Sim card my mom wants back because my mom refuses to pay for her phone. My sister is 16 this year.

Since I'm the only one with contact with my sister, I need to get the Sim card. She's already going to give me the iPad back for my mom, but she doesn't know about the Sim card.

I am 18 now so I'm worried shell make something up about me too.

My current phone used to be my sisters, but she begged me to give her the iPhone my mom want going to give me, and stupid me gave in. My phone is malfunctioning badly due to age, and my mom wants the Sim to upgrade so I can have a working phone. And that's also going to cause tention.

My mom is still paying my phone bill because there are limited jobs in my town, and every extra cent I make I use on my service dog, so its not like I can stop doing that.

She's also helping me find a job.

I need a way to get the Sim card.

Tips?

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