AS we know Mother Caramel and her children were devoured by Big Mom. What If big Mom uses Prometheus as the big brother that cannot abndon her, and Zeus as her little people that keeps her family close. As, Prometheus was first created by mother Caramel in order to make peace with the giants, Big Mom may have created her version in order to have him close and remind her of that day. Zeus may have been created as her little brother in order to keep intruders away form her family as he can help create massive storm.
I believe that Big Mom created these two Homies as the ones that as a part of her cannot run, cannot abandon her and could not be hurt by others. As we know Prometheus was never injured until Brook wounded him. This could have been the case because Big Mom couldnt bear to lose him and used her own strength to power him as such. I also believe that As a part of her soul she knows thery can never leave her, something Big Mom is obsessed with. Big Mom cant bear crews leaving her, and cant tolerate her family abandoning her so she beats abuses and blackmails them. In the case of Prometheus and Zues they are tied to her forever and cannot have the will to leave her permanently. Thus she will never have to risk losing them and the memories that they are associated with. As such Big Mom holds onto these homies as her right and left hands both metaphorically and psychically using them as council and as the brother that represent her lost family , and the family that could not ever want to say goodbye.