If multiple creatures deal combat damage to you and to a planeswalker you control simultaneously, Vengeful Pharaoh will trigger twice. The first trigger will cause Vengeful Pharaoh to be put on top of your library. The second trigger will then do nothing, as Vengeful Pharaoh is no longer in your graveyard when it tries to resolve. Note that the second trigger will do nothing even if Vengeful Pharaoh is put back into your graveyard before it tries to resolve, as it's a different Vengeful Pharaoh than the one that was there before.