How to import object with multiple relationships?

[pammurillo]

Hello!! We are trying to import records of Product, PricebookEntry and a custom object (also related to product) to a new sandbox.

For some reason we are not getting products with both related objects, instead products are duplicated. Some of them will have pricebook entry and the others will have the custom object.
-Edit: Since it is a sandbox, Product2, Pricebook2 and PricebookEntry are prepopulated on the refresh. So that might explain the duplicate values.

What we don't know how to handle is the import of the standard pricebook. Since we already have one in the sandbox, once we try to import another "standard" pricebook it will be isStandard=false, so we will get a "Before creating a custom price, create a standard price" Error. Can we somehow make this new pricebook standard or can we use as reference the existing pricebook?

Thanks!