How do I, a person who deals with being excited and anxious by getting overwhelmed, teach my kid how to deal with being excited and anxious in a different way? I have no idea.

The other parent isn't helpful (doesn't get excited and anxious in this way).

#ActuallyAutistic

@quidcumque maybe by reflecting such situations with them. Telling them what went on inside of you, what you would like to be different or what you perceive as difficult or why you are totally fine with your reactions but other people are not and how you deal with these people then?
@Mama123 I think I am quite good with reflection afterwards: we usually do that! I'd love to have something to teach them to calm down *before* a big meltdown happens (because they do happen, and it's starting to affect the siblings negatively).
@quidcumque ah, I understand. Well, I think it might be an awareness thing that can help in the long run. So the kid learning to notice when its getting in the direction of a meltdown. In this case you can do that for them, when you know they are starting to get anxious. And then "feel" the feelings and observe them with curiosity and eventually coming up with individual coping strategies.
So for example my K2 always got really mad (screaming, hitting, destroying things) right after school. We sort of did the above and we came up with his solution, which is: whenever he feels like that after school, he eats the rest of his snackbox. And yes, that was a simple one, so maybe not the best example.
I think that this usually takes well into adolescence for bigger issues than the one in my example. I'm sorry that I don't have a better short term solution.
@Mama123 it's good to hear that there are longer term solutions though! Hunger is a trigger here too, and we actually do the same snackbox thing!