This depends on your local council, i work for the elderly team in social service and talking for my borough no he wouldnt have to move out. You may be able to apply to your local social services and be assessed for funding.
I have dealt with referrals for many clients who live with their children, and as far as i am aware the relatives have not had to sell the home they are still living in, this has only happened when the client owns their home and been living their oin there own and wanted to apply for residential care privately.