Hi Virgo!

This is indeed funny. The agents you named are from house telvanni not from the thieves guild. So no problem here. You can kill them without any problems....

...BUT: You will eventually ran into the famous codebook quest. This one causes a lot of troubles because: Eidis Fireeye (the head of Balmoras fighters guild) wants you to get a codebook of a member of the balmoras thieves guild. If you aren�t very good in pickpocketing you have to kill her and therefore you fall out of the thieves guild.

The best solution to this is to make your fighters guild quests in Sadrith Mora.

bernhard live and let die!