I get the feeling that the Eye of Tor is actually the gate that the Forsaken want. And that your grandfather is the leader of the Forsaken. As I collected more and more shards the description of the mirror gets darker. I don't remember what they all said but I remember feeling uneasy. I don't actually remember what happened to the grandfather but the fact that he survived the empire's fall when he was the greatest mage and the fact that he only died recently is weird. You would have thought the beasts that ruined the empire would have killed him too. I don't know why they would want you or your sister if your grandfather is alive. Maybe his blood was corrupted some how and they need some from a pure source. Maybe it is like Pirates of the Caribbean and he became a lich before they knew they needed his blood. I just get an odd feeling as I build the mirror. Like I am doing something wrong or evil. Another note is the shards are called black shards. Black is usually associated with evil. If they weren't tainted or evil you think they would be called mirror shards and look like a shard of a mirror.
EDIT: Maybe the forsaken didn't actually take your sister. Either she escaped or the good version of the forsaken rescued her.
EDIT: Maybe the forsaken didn't actually take your sister. Either she escaped or the good version of the forsaken rescued her.