Two brothers, whether separated by a significant age difference or not, are going to pretty much lead to the same result.
Teasing, nagging, revenge, and those sorts of less commendable qualities.
But it would seem more a question of how often, and how deep, how chronic I guess, those qualities emerge or go, when in the presence of the sibling.
With these two, I can assure you it happens enough to lead to times of sheer exasperation on the part of their long-suffering parents.
But while I might not be a good judge of where, exactly, this degree of misbehavoir and ignoble attitudes falls on the big scale of "normal", I do know this: when they are in harmony with each other — soft, gentle beyond description, with love pouring out of their eyes, and in their every movement, even if it just lasts for a minute — it is enough to make a parent's heart pierce with happiness.
If a parent ever despairs, it is these moments that one must hold onto, and foster. For there, surely, is the answer to all things.