How should I behave to my girlfriend's toxic sister?

[Anonymous]

We're neighbours. Me and her sister were very friendly. But, she hates our relationship for unknown reason and is trying her maximum to ruin our relationship. She's two faced. Acts nice infront of me. At home, she spread gossips and negatives about me nd creates a bad image on her parents mind. So now they hate me too.

Next month she's gonna join a new company which is in a far away state. It will a long journey and strange place. Her father is abroad and my girlfriend have uni exams. So she called me and my mom to accompany her and her mom.

How should I behave?

Should I act nice and friendly (which might benifit my relationship )?

or

Should I behave formally?

[KrakenAttackin]

Why TF would you agree to go? She is your enemy and that won't change. Let her be an adult and move to a new place by herself.

[Asker]

Because we're family friends too and except this relationship thing, all of us are very friendly.

[KrakenAttackin]

Asker. You are setting yourself up, bro. You won't be able to win with this chick.

[Asker]

Yeah buddy got it. Me too not interested, But the trip is unavoidable 😬

[KrakenAttackin]

Asker... I'm that case I would keep my distance from her and NEVER be alone with her. Also, let someone else know what's going on.

[Asker]

Yes. You're right. Thanks a lot

[spartan55]

I wouldn't do it. Don't go

[Asker]

Yeah I cannot escape from it. Because my mom doesn't know about this problems and our families are very close

[spartan55]

Wtf, you cannot escape? Wow... you are old?

[spartan55]

Nothing good can come out of that trip. I take it the sister doesn't have a boyfriend?

[Asker]

No. She's divorced.