It depends on whether you and your brother own the house as joint tenants or tenants in common.
If you are joint tenants, you both own the whole so cannot take a secured loan or any other form or debt against the property without the consent of the other.
If this is the case and your brother agreed, he would be equally liable for any debt if you defaulted.
If you are tenants in common you each own one half. You can mortgage your half, or raise money against your half, independently of your brother.
However, it may be difficult to find a lender because it would be impossible to get possession of the house if you default.