If the original loan application clearly stated that the property was going to be your family home then they should not have appointed a Receiver: They are obligated to go through the MARP process and then apply to court for a possession order.
The rent a room scheme would not be considered commercial.
You should really see a PIP to obtain advice on all your options. The MABS offices provide a great service, but sometimes they do not see the benefits of a PIA.
Jim Stafford