Demon Slayer: Alternate memories

We all know the backstory of the twins, Muichiro and Yuichiro Tokito. A story of two twins living in the mountains by themselves after their parents' death which in the end, one of the twins died due to a demon attack protecting his brother and the other twin lived up to be a hashira. A short simple summary of the backstory of Muichiro Tokito. But what if they had a friend before that moment and had the same experience? What if Yuichiro lived throughout the demon attack and became a hashira with his brother and his friend? What will happen then?