An RDSP must be established only to be for the benefit of the beneficiary. So RDSP issuers, which are in general the major financial institutions, do what they can to ensure that when withdrawals are made from an RDSP, the payments go only to the beneficiary or in respect of their legal representative.
As a temporary measure allowing certain qualified family members, the scope is limited to parents and spouses or common-law partners, generally on the basis that those individuals would have the best interests of the beneficiary in mind. So a broader scope might have opened up possibility that yes, indeed, a priori, there might be some uncertainty about whether they had the best interests of the beneficiary in mind. But the expectation is that parents and spouses would have the best interests of the beneficiary in mind.