I would not rely too much on the council. They don't have a duty to rehouse people unless they qualify as priority need, eg under 18, pregnant, vulnerable, etc. It can even be difficult to get rehoused if you do qualify.
If your sibling does think of turning to the council, they need to stay in the area where they have a local connection. They should also stay in their current property until legally forced to leave, or they will be classified as intentionally homeless.
It might be worth suggesting that they approach Shelter or local homeless charities, if there are any. They will get good advice, at the very least.