Meta: the point of this site is conversation. You don't have to respond. With an open question like this is probably best to assume the asker means "who #in your opinion# gets too define those rights".
Also, yes legislative bodies. But in eg USA that means a corp like Disney pays to draft the law and pays legislators to vote for it.
On a site like this that is very American-centric, where moral rights are not as known a thing as in other countries due to different legal traditions, it was reasonable to assume the OP was unaware that moral rights are a clearly defined concept in legislation already, not something vague and up in the air. If the OP wants to formulate their question more clearly, they can.