Probably not. As per Income Tax Folio S1-F4-C2 s.2.47, For an individual to claim the eligible dependant tax credit, a person must be wholly dependent for support on the individual. Support involves providing the basic necessities of life, such as food, shelter, and clothing. Wholly dependent for support on the individual generally means the person is financially dependent on the individual such that the individual provides almost entirely for the person’s well-being. In the case of a child, to be considered wholly dependent for support on someone, that someone must be responsible for the usual day-to-day activities of raising the child, such as ensuring the child attends school, and providing necessities such as food, shelter and clothing.

So, you would have to be able to prove that you are your brother's caregiver, not your parents, in order to be able to claim the eligible dependant tax credit.