Hello and thanks for using Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
An Executor is under a duty to act in the best interests of the beneficiaries and to act in a reasonable and prudent manner. The fact that your sister has now vacated means that there is no reason why the property should not be put on the market straight away. Your brother's argument that he wishes to wait for the "housing market to improve" holds little weight, as it is unlikely to improve especially as the winter months will be upon us before you know it. Furthermore,while the property remains empty, there is an issue whether you can arrange suitable insurance and you will be responsible for any outgoings/repairs while it remains unsold.
It would be normal for 3 valuations to be obtained, and the fact you have 4 is more than adequate evidence that the prperty should be marketed for £45,000 or slightly more, with a view to obtaining £45,000.
In a situation where an executor is acting against the interests of the beneficiaries, an application can be made to the court to have him removed and for the other executor to act alone.
This would of course be an expensive and unpleasant route to take, but I would suggest that you write to your brother explaining the above.
Alternatively, you should instruict solicitors competent in Probate law without delay, and ask them to write a letter to him.
Hopefully, the mere threat of Court action will make him see sense.
I hope this assists and sets out the legal position to you.