Nepos, as it turns out, has been doing several jobs at once for twenty years. The old man is overburdened and very tired- but not about to let himself fail. Nepos, apparently, is one of the Forsworn- who are called such because the Reach is their homeland, and they cannot claim it. They had a great rebellion during the war between the Empire and the Aldmeri Dominion, one which seized back control of the Reach- but as soon as that war ended, Ulfric Stormcloak and his men came in and flattened the rebellion utterly.
The bald man has no idea how, but apparently the Forsworn King, Madanach, survived the rebellion and being thrown into Cidhna mine- he recieves orders from his king every so often, and follows them without question. Nepos considers it a great irony that Madanach continues to rule from within a Nord prison, directing Nepos and urging the poor and downtrodden of Markarth to join the Forsworn rebellion.
Of course, the reason he’s willing to tell you all this is that he’s sure you’re not leaving alive. His servants, even the housekeeper at the door, are all Forsworn agents, and you are far from the first to reach this point in an investigation. And, he reassures you, you will not be the last, either.
When you leave the conversation, Nepos rises to his feet, preparing to attack, even as his servants give out their battle cries and rush to assault you from behind.
Nepos is a strong Destruction mage, using a sword alongside extended Novice-rank streams of fire or ice to wear you down, and his housekeeper likes to shield herself with Transmutation. The other two servants just come at you with weapons. This would be a frighteningly dangerous fight if not for one thing- all four of them are wearing only regular clothing- not even enchanted. This makes the fight a bit of a test of your ability to focus on one target at a time, but otherwise not all too threatening.
Once the lot are dead, you can ransack Nepos’ house if you like- but if you do so, find a place to stash your take before continuing to Eltrys. Otherwise you’ll find yourself out of luck on keeping any of it when you reach the next part of this questline, as there’s an unpleasant surprise waiting for you in the Shrine of Talos.