Costume ideas for brother and sister!

Ok so everyone is always super impressed with my costume choices. Not that they’re anything special I just don’t tell them what my daughter is going to be and just have her show up at grandmas or whoever’s door and I think the surprise adds to the cuteness? Anyways, Well my son just turned one so this will be his first time trick or treating and I want to do a “matching costume” I was thinking Danny and sandy from grease but I want more ideas! With pictures if you can? I also thought my son would be a pretty cute Elvis since he is such a flirt and has long hair we could slick back 😂 but I don’t think there’s a matching girl part that my daughter could be. They are 3 and 1

I’ll post pics of previous costumes and my son so you can help 😜

Thanks!