so kelly and matt having brother energy - i feel like most of the time matt is absolutely the big brother. he has oldest child energy (despite being younger than his actual sibling). he seems like he has his shit together, reliable, responsible, the one put in charge when dad's (boden's) away. HOWEVER, kelly definitely has big brother energy as well because he is - we saw it with katie. he's fiercly protective, will drop everything to help you etc. but, here me out, kelly has more middle child energy 😅 usually finding himself in trouble even though he's doing his best, a hothead... i cant properly explain it but please tell me i'm not crazy 🤣
Kelly and Matt definitely have brotherly energy!
I feel like your opinion on who has oldest sibling energy can really depend on if you have siblings or your experiences with people who have siblings.
For example, I'm the oldest child in my family and unlike Matt, I do not have my life together right now. However, I think that being protective of my sister and always being willing to help her is something that kind of defines me. As you mentioned, Kelly also seems like a protective person and that's probably why I think that he has oldest sibling energy.
In contrast, my younger sister thinks that Matt has oldest sibling energy because he's more responsible. Like I said, your opinion depends on what you think is the most defining trait of an oldest sibling.
As for Kelly having middle sibling energy, I think you might be onto something! My new headcanon is that Andy had the most oldest sibling energy, Kelly was the middle, which left Matt as the youngest. Because I honestly thinking that despite how silly he was, Andy was the most responsible out of all of them (he had a wife and kids!)