Oblivion:Separated at Birth

Quick Walkthrough
# When asked about rumors people in Chorrol might mention that they saw Reynald Jemane in Cheydinhal and that he was acting strangely or ignoring them.
# When questioned, Reynald claims to know nothing of this. He gives you 50 Gold and asks you to travel to Cheydinhal and find out who is acting as him.
# Asking about Reynald Jemane in Cheydinhal leads to one Guilbert Jemane, who is currently staying in the Newlands Lodge near the west gate.
# Guilbert informs you that Reynald is his long-lost brother and he then travels to Chorrol to meet him.
# Talk to Guilbert Jemane in Chorrol, he'll give you your next quest.

Detailed Walkthrough

Chorrol
If you walk around Chorrol and ask the locals about 'latest rumors', pretty quickly you'll hear about how some of them have seen familiar Chorrol resident Reynald Jemane walking around in Cheydinhal. Strangely, when the locals spoke to Reynald, he acted quite odd. Sounds like all this might be worth investigating. Go speak to Reynald. Apparently, he is also aware of these rumors. He gives you 50 gold and sends you on a mission to Cheydinhal to deal with the impostor.

Cheydinhal
Once you arrive in Cheydinhal, once again, rely on the locals to tip you off on to exactly what's going on. While none of them have ever heard of a 'Reynald Jemane', they have heard of a local resident named Guilbert Jemane. It doesn't take all that much looking around to find Guilbert, and he's a spitting image of Reynald. So speak to Guilbert, and he'll tell a bit of his family's history, which makes it clear that Reynald and Guilbert are long lost brothers. At this point, Guilbert will leave for Chorrol to be reunited with his brother. Go back to Chorrol yourself, and find Guilbert. He'll ask you to do him another favor...

Notes
Sometimes random NPC will chatter with each other. If you are close enough to overhear them and they are discussing the odd behavior of "Reynald", you'll get an automatic "topic" update and can then ask around about him. You might have to do other topic quests first before NPC start discussing him.   
Once the quest has started, you do not need to talk to Reynald before you go to Cheydinhal and tell Guilbert about his brother. However, that means you will not get Reynald's 50 gold. So if you don't want to miss out on any gold, make sure you go see Reynald before you leave Chorrol.
You can follow Guilbert to Chorrol. He runs fast but stops every once in a while. Your green arrow marker will stay locked on him, though, in case you lose him. Many things along the road will attack him. He is flagged as essential so he will fall unconscious instead of dying. At certain levels, looting the dead attackers can be very profitable.
Although there is supposed to be a unique dialog if you follow them until they meet the first time, this often gets disrupted by the fact Reynald can't pull his face away from a tankard long enough in The Grey Mare to get up and talk. Using a combination of nudging characters out of the way, "waiting", and reloading from saves it is possible to un-bug this by using "wait" until 12:00AM - not approaching Reynald when Guilbert is present (so you don't trigger the quest update and miss the dialog). He gets up out of his chair and begins to walk to the door at this time, running into Guilbert on his way. The quest update and dialog should happen when they are in speaking distance.
The dialog is as follows: ''R: "What? Who ...? (Oh) Damn, not this again. Wake up! Wake up!!" G: "You're not dreaming, Reynald. It's me, your brother, Guilbert." R: "That can't be, I don't have a brother. I mean, I never knew my real family. Who did you say you were again?" G: "I am your twin brother. When we were very small, our farm was attacked by ogres. My ... our father and I escaped."  : "We thought you and Mother had both been killed. If we had only known!"  : "All I know is that traveling merchants found me in the wilderness by the body of my mother. I was raised by the monks at Weynon Priory."  : "My brother! It is wonderful to see you again. We will have much to talk about in the next days."
The confusion about the dialog is Guilbert seems to have been intended to deliver two lines in a row, but Reynald speaks them instead. (Reynald never knew his real family, therefore him saying "We''' thought" makes no sense.) The events are explicitly clarified by speaking with Guilbert after.

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