To find out who are the owners of a property you may use publicly available information on the Land Registry website https://www.gov.uk/search-property-information-land-registry . A copy of the property title can be purchased for £3 there. Alternatively, you may ask a solicitor or conveyancer to assist you in obtaining of this document. After you receive a copy of the title, you will see the names and postal addresses of the owners.
If the owner is diseased, please use the probate record service https://www.gov.uk/search-will-probate to find out if the diseased left a will and who the executor or administrator of the estate is. In addition, please check records in the London Gazette https://www.thegazette.co.uk/wills-and-probate and on the Internet as often when people die information about the death is published in the Gazette or local press.