Iirc, They didn't know how to treat franz as baby after their mother died. I think In the novel one of the brother actually talk about it. They doesn't know how to do with franz so the leave him to the maids, i think they're grieving too. Their father always busy with works, of course they're busy too. They feel bad when they see franz playing alone but they still didn't know what to do with him until franz approached them first, they finally know they just need to be with him and loved him. That's why now they spoiled him and do everything to make sure franz being loved. Even though they're still busy they still at least has time to spent with him

The family is so cute
So I kinda don't understand the first few chapters. Why did they ignore Fran in the beginning? Until he got the future and start to actively try to change the story, why did they ignore him. Its so offhand for their characters.