Reader's Mail: My Siblings Act like Sworn Enemies, Not on Speaking Terms At All!

Hello PCB readers, please I need your advice. Has anyone here ever had to deal with siblings who just can't stand the sight of each other?  

My two younger sisters HATE each other! They have stopped speaking to one another. Everything one of them does obviously irritates the other. One walks into a room, the other walks out. One of them coughs, the other hisses. Everyone in the family has tried to
settle these two but it's just not working, none of them will even tell you - okay this is the very GOOD reason why I don't like her or I'm annoyed with her. It's so crazy and annoying now. I feel it's a deep seated jealousy thing, kind of started since they were kids. Now that they are adults, they still won't get over it.  

A problem shared is a problem half solved. Please, what would you advise?