Thank you. That may be the reason.
Technically, the tenant may sue the owners of the property to get relief. By entering into the contract for the property, your brother had agency to bind you as well (arguably). Agency is when one party speaks for another:
EXPRESS AGENCY - the agent has actual authority from the principal. Example is the power of attorney.
IMPLIED AGENCY - the agent has implied authority from the principal. An example would be an director or officer of a company - while they are not expressly representing the company, it is implied they are, and anything they sign would be binding unto the company.
APPARENT AGENCY - that there was apparent authority. Example is if you walked into a store, and asked how much an item is. A person who worked there told you $40 and rang you up for $40. Later you find out that the item was actually $150, and the employee did not even have the right to ring you up. Regardless, they had apparent authority to you, and the price quoted by the employee with the apparent agency is binding upon the business.
Ergo, the lack of privity can be overridden by agency if they can prove that he HAD agency to speak for both of you.
But that still does not explain why only YOU are being sued. Perhaps because they think you have more assets for judgment. Someone in your situation can still make other nuanced arguments of course and may be able to win the suit - it really depends on the situation. But I am guessing that the above is why they are pursuing you, specifically.
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