But he has a lower position then the maids and the sisters abuse is increasingly a problem with how strong she is
No, he isn't lower than the maids. The only time the maids go against him is when it's against the orders of his parents. Like going to eat his meals or going to training. And again, you are ignoring the fact that it's exaggerated a bit for comedy.
Also, it's actual training and sparing. It's not like he's getting any serious damage or anything seriously bad is happening.
While he does have a moment where he's knocked out, that's supposed to be humor that we as readers shouldn't take too seriously.