You can just make one choice if you wish. I think the UCAS fee is lower if you only choose one. Once your application has gone off, you can add more choices later if you wish (though this will incur the full fee).
Universities generally have accommodation available for people with additional needs, which may include room for a carer, or special access arrangements. You would need to make enquiries with the student support services or the accommodation office at the university to see whether they could meet your needs.