As per the topic:

One example is the background package is Void Commercia in IH which includes Common Lore: Imperium. Adepts already start with that skill. How you you solve this? Give the player +10 or Talented to that skill or another in the package? Lower the xp cost, remove one alt. lower both Characteristic penalties?

Another example is the Volg Hiver background. It starts with Melee Weapon Training (Primitive) - just like all classes that character can pick. Is an increase in WS of +3 to +5 appropriate to reflect this, or should I allow the player to pick another of the starting weapon talents (primitive, SP or las)?

Those only exist to reflect that the character starts with those skills and talents. You aren't supposed to buy them again and doing so won't get you anywhere as per RAW. I'm not sure why FFG think it's necessary that they be there.

I think in rogue trader or something there is a ruling, that if the character gets the same talent twice at character creation, he instead gets talented (any). Also having skills from different sources should stack; characters should get +10 to that skill if they have same skill from two different sources, or +20 from three.

I dont know if thats how it is, I belive it is. If its not, as a GM I would make it so.

Amaimon said:

RT used the character path system and due to that they allow duplicates skills to give the + or Talented.

DH does not allow for any free bonus from duplicate skills and talents. If your home world and class give you the same talent or skill, they overlap and you gain no bonus. Individual GM's might house rule this otherwise.