Hi RafaelGascaCalvo,
There are two table, I see that NJ also mentioned, INV_FLAT_HIERARCHIES or INV_HIERARCHIES which keeps the relation between the parent and child investment objects' stored in the database. Try to check if you can create a GEL Script in such a way that whenever the row for a Requirement object instance will get updated, a process will trigger and do the needful. I am not sure if that is possible and atleast you can give it a try. Hope that helps.
Thanks,
Abhisek Dhar