It is possible to convert a single family home into an HMO. If you are not in an Article 4 area, and therefore benefit from permitted development rights (PD rights) you can in most cases, and subject to other planning constraints convert a C3 dwelling into c4 (HMO) up to maximum 6 people. If you wanted to go over this number of occupants, you would require a sue generis planning application to be submitted to your local planning authority. In the UK, the process for converting a single family home into an HMO is governed by the Town and Country Planning Act 1990 https://www.legislation.gov.uk/ukpga/1990/8/contents and associated regulations. You should research the requirements and seek the necessary approvals before proceeding.