Is it necessary to inform one's parents about the sadaqah given on their behalf while they are alive, and is sadaqah permissible only on behalf of parents or on behalf of anyone?

It is not obligatory to inform the recipient about the charity, nor is it a condition that the charity be for a close relative; rather, it is permissible for both close and distant relatives. The reward for any act of worship a Muslim performs and dedicates its reward to another Muslim, whether living or deceased, reaches them, even if the one performing the act does not know the specific individual for whom it is intended, similar to supplication (du'a) and seeking forgiveness (istighfar). Charity is accepted and beneficial for parents and others, and it contains great good for both the living and the dead.