An interestingly complicated tale which highlights also the issues arising from (let's guess deliberate?) non-finalisation of probate, given that the previous owner died in 2005.
What CPOs are for? An interested party could reimburse the costs falling on tte council. Also, the executor is entitled to sell assets on behalf of the estate (in England at least) so the fact that the estate has not been finalised does not prevent a sale happening.