To not look after my niece and nephew as it means dealing with a horrible SiL?

[howfartospar]

My SiL can be very opinionated, bossy and falls out with lots of people.
She has been horrible to me previously and now I keep her at arms length for the sake of family peace.
My brother is quite hen pecked and I'm unable to just deal with him.
She's recently asked me to start babysitting my niece and nephew overnight. My issue is this would mean dealing with the SiL again and I want to say no. AIBU to do this and if not, how do I say no without it causing more arguments.

It would be for overnight Stays when they want to have a night out or a weekend away.

So they just want to use you as a free babysitter whilst they go off on child free weekends regularly.
What exactly do you get out of this "arrangement" other than stress of dealing with your sil and being at her beck and call with all the drama when you can't do whatever weekend she demands. Also how did they ask or did they just tell you that they want/expect you to take over for their current sitter

Hi sil. Bit confused why you want someone as awful as me around your dc regularly...
Regards op.

Surely they just do what anyone else does who can't sort a babysitter - have fewer nights out / weekends away etc?

Why would you agree to do regular favours to someone who has previously been really horrible to you?!

Just say, no thank you-I don’t want to provide free overnight childcare for anyone.

In that case no, I wouldn't do it at all. She's got to learn to be nicer to people if she wants favours from them.

This.

Date nights aren't an emergency.