I have two DDs 3 & 4). They are very close in age and always had the odd argument over sharing etc. But since eldest DD has started primary school they seem to have really fallen out. When DD is home from school, within five minutes, they are arguing, crying and can't be within a foot of each other. I have tried to emphasise the importance of being kind to each other and being good sisters but they don't listen. I'm tired of being a referee 24/7 and worry about their relationship (I know they are still very young). They used to have such a good bond. DD1 gets upset that she can't go to school with DD and this could be a big part of it? When DD2 attempts to be loving or nice to her she just totally rejects her. DD2 seems to be jealous of her sister, she has hearing difficulties and wears hearing aids and also is always back and forth from children's hospital with duplex kidney complications. She has asked me on several occasions why big sister is never poorly or can hear well. Am I overthinking this? Any advice would be greatly appreciated.