I don't think the father is decent at all. It can be seen that the father already knew that the older brother was abusing the younger brother for years (we know this because it was mentioned that the younger brother would go to the annex where the older brother was, every month for one week and it was only recently that the servant found out that abuse was going on). I think the only reason the father decided to take action this time is because he found the younger brother useful because if his paintings in comparison to the older brother and I am guessing that the younger brother must have threatened to harm himself or told the father that he couldn't continue painting if the servant died.
So glad the father is decent… atleast one family member pays attention