COVID-19 life span of the virus in an infected persons accommodation.

I have relatives in the UK that need to enter a covid victim's flat, he tested positive just after Christmas and was self isolating at home until he became seriously ill, he was taken to hospital on 30th December and he passed away a few days ago.

My question is how long can the virus survive in his flat ? His flat has been unoccupied since 30th December, the heating has stayed on since he was removed, relatives need to get to his safe to retrieve his will and other documents, birth certificate etc, they are very reluctant to enter, I have tried to reassure them that the risk now is minimal, unfortunately the NHS, Dr's Surgery & Environmental health have been of no help, can anyone point me to any links that may give the relevant information, thanks.

I would also hope that you will all be somewhat respectful in your replies, I know many of you consider this virus to be a conspiracy, any attempts of that nature will be reported. Thanks in advance for your help.