Young son annoying at home, shy at school

Looking for some help for my eldest son - 4yo (nearly 5).
He did early entry to school this year, so hes youngest of the class. He was teary for the first week, but once hed found a friend and familiar face, he was sorted and has loved it ever since.
Hes always been intelligent, could count and do ABCs from young age, quick to walk (9mths), etc etc. Although was very stubborn about toilet training so finally happened at 3yo. He seems a lot more grown up than some of his similar-aged cousins. Weve always been able to sit him down and explain a situation, and hed understand or comply or wait or accept a compromise, whatever it may be were requiring.

Hes a pleasant child by nature - was always obliging, willing, loves one-on-one attention, kind (would have given me HIS piece of cake in the past).
He is also quite sensitive, and potentially a bit insecure? Tells me multiple times a day that he loves me.

However, since starting school his behavior at home has changed noticeably. He is quiet and shy at school, not wanting to be centre of attention and certainly wouldnt want to be naughty in fear of the teachers authority. However at home, he is constantly annoying his younger brother (3yo - only 20mths younger) and acting out. He will not listen to me, disobeys, annoys his brother, argues etc. It feels like I am constantly refereeing fights and growling, particularly the 4yo as he is often the one who starts it. The only way I can get response from him is being VERY firm and absolutely meaning what I say, like a ton of bricks coming down on him. His worst threat is that I might tell his teacher how hes behaving. There have been a few violent outbursts of striking out at his younger brother - weve since found out that one child at school had been hurting him (unprovoked) and my son would walk away. He didnt seem bothered by this too much, and has seemed to have forgotten about it since I discussed with teacher and said child was reprimanded.

2023 was a very busy changing year for us - we moved out of our family home, lived with family, rented two different places, and brought a new baby into the family. Both of my boys were exceptionally adaptable through this all - they are extroverted and seem to thrive on busyness and always doing things... in fact the first thing the 4yo asks me every single morning is what are we doing today. He loves routine, knowing whats coming next - school has been the best thing for this.

As a baby he cried 24/7 for the first 4-6mths, which was put down to colic. He had noticeable stomach pains with the drawing legs up etc. Weve used chamomilla successfully over the earlier years, and also lycopodium here and there.
He very easily gets croup, is sensitive to the wind.

Id love to know his homeopathic constitution someday, but for now Id love to curb his aggressive/noisy/annoying home behavior and bring the old self back out in him. If only hed just play with his younger brother peacefully instead of always trying to provoke a reaction. When they do play together, theyre best of friends.
[Edited by ozkiwi on 2024-05-29 00:56:42]