Unfair play

Nedbank executors of my Parents estate have chosen to honour the claims of my sister to the tone of close of 1.5 million rand because of an e-mail. Nothing states this in the last will and testament of my parents.I believe they are doing this not due to reason or evidence but due to ease of settling the estate ie financial gain. Its a very weak case and they have set it up that agreed to a sale of property ..then advised me about the claim ..after I gave them confirmation to sell the property.I now have to go to court. I feel snaked by them and now have to take legal action against it. it seems banks are about money not about being executors at least in this case. Really poor review shocking have to say that the first executor under nedbank did her job but now the new executor I feel has been brought in to settle things ...and this option has been the easy way out not the morally correct one.