Be her brother Jackson not her dad.
*seeing trying to reason isn't working I get a stern tone*
Jackson listen very carefully while you are here you will be a child. I do not allow children to act like adults in this house you will be a brother to Amber and that is it. You said u spanked her before well as of today that will no longer happen. This is your warning. You will not call her stupid not dumb EVER again and if I hear it you are in big trouble young man. This will stop. You are 11 years old and I promise you will act like it you are not grown.
*softens my voice* now Jackson that was your warning, I want you to know that you and Amber will be safe here and you two will be able to have fun and do what children do you will have a nice life while you are here I will make sure of it I and the other adults in this house will protect you
*only reason I got kinda stern is with kids you have to be stern sometimes and stick to your word but also reassure them that they are safe and you care I think to myself *
And you should trust me because I really do care about you both and I will make sure nothing bad happens I promise u have a place to stay food to eat u got clothes shoes and everything it's not bad at all. Please at least try to trust me ok? We will work together