Hi S,
When you load hierarchies you need to specify which hierarchy to use for PARENTH1/2/3
therefore you won't be able to overwrite one another unless you tell it to.
In your question you said you have 2 hierarchies in BW, do you want to load both? or just one?
if you want to load both then you need to create PARENTH3 and PARENTH4 to cater for both.
Andy