Hi Dwain
Welcome to the forum, you might want to have a look at the following FAQ which explains where everything is.
Welcome to Benefits and Work Thank you for your question, unfortunately it is out side the remit of the forum which does not cover housing issues.
You need to contact Shelter to get any housing advice;
england.shelter.org.uk/get_help What should happen is that your friend may have a statutory right to succeed his mother's tenancy, if he is under-occupying the property the landlord may seek repossession on the grounds that "suitable alternative accommodation" has been offered.
The housing association should offer him a one bedroom property, unless he needs over night care, in which case he will be offered a two bed property. He needs to make sure the property he is offered is in an area where he wants to live as once he accepts a property it will be very hard to move if he does not like the area or the property does not suit his needs.
He therefore does need to seek legal advice before he does anything or sign anything.
Gary