Executor neutrality in removal claims

Imagine the following scenario. You have been appointed as executor by a long-standing client, who has recently died. Two of her children do not get on. The daughter argues that at a time when her mother was suffering from dementia and her capacity was therefore in doubt, she entered into several lifetime transactions which benefited her brother and his family. The daughter says those transactions should be investigated and argues that because you advised the mother in relation to the transactions, and because you are in any event biased in favour of her brother, you are not sufficiently detached and independent to investigate the transactions properly. She therefore asks you to resign as executor in favour of an independent professional. On the other hand, the brother and his family argue that the sister’s accusations are wholly without merit and that you should stay in office. What should you do?