In his speech, Mankar Cammoran says that Mehrunes Dagons realm is Dawns Beauty aka Tamriel, but he also says that it's Lorkhans? Whose is it?

He said Tamriel belonged to Lorkhan. Magnus leaves and returns to liberate Tamriel, from the lieutenants of Lorkhan, as Mehrunes Dagon.

http://www.imperial-library.info/obscure_text/aldudagga.shtml#1. As you can see, MD had a hand in creation as the being known as The Leaper Demon King. But, LDK got eated and became Mehrunes Dagon, and is now forced to destroy all (impossible task mind you) before everything can go back the way it was.

I dont get it, Magnus is Mehrunes dagon?

And it seems in his speech, that Mankar Cammoran is somewhat aligned to all the deadric princes, including Lorkhan.

Read the first portion of the The Seven Fights of The Aldudagga I linked above to start getting a sense of what Subadim means. Once you read it, somewhere around here Subadim brought up the argument that MD is likely to be Magnus (though, I still have my doubts)

Was Magnus. They're different now. Even in the Commentaries, the pieces of Magnus - the Magne Ge - form Mehrunes Dagon.

Is that text canonical? I'm also finding it a bit hard to understand, tbh.

yes, it is. its not the easiest text ever, but if you take it slow and compare against other texts (varieties of faith and the monomyth are probably most useful) you should be fine.

Allright. I'm not a lore buff, so I haven't read that much of ES Lore, and im not sure i have time to dig into it really. The only thing I want to know is where Mankar Cammoran stands with the Daedra and Lorkhan, and how they are related? So if anyone can give me a simple explanation (or as simple as possible ) I'd appreciate it.

EDIT: How Lorkhan and the Daedra are relatded that is.

Mankar uses Dagon, which is the concept of revolution, to overthrow the evil Empire. Lorkhan seeded the world with the Daedra.

I'm confused. Where does that leave Meridia?

There was no Meridia, until Magnus entered Aetherius and a rogue piece of him re-enters Oblivion.

I give my soul to the Magna Ge, sayeth the joyous in Paradise, for they created Mehrunes the Razor in secret, in the very bowels of Lyg, the domain of the Upstart who vanishes.

The domain of the Upstart is the stomach of Alduin, in the Aldudaggavelashadingas. The Hungry Stomach in Satakal is Lorkhan. The Upstart who vanishes is Lorkhan. His domain is the lesser of the two voids, Oblivion.

Okay, my mind, it is blown.

Let's see if I have the gist of this:
1. Magnus leaves after creation. He manages to escape to Aetherius, but also smashes into tiny bits, becoming the Magna Ge, who also escape to Aetherius.
2. The Magna Ge are the Leaper Demons the Nords talk about, and although they escaped to Aetherius, they also didn't.
3. 99.999% of the Magna Ge/Leaper Demons combined into Voltron Mehrunes Dagon, while the remaining 0.001% became Meridia, and they went off to live in Oblivion.

Is that about right?

Yeah, but remember that Magnus is the Sun too, so one really big piece and thousands of smaller pieces.

I know you knew that, but for the sake of clarity.

The Magna Ge gave Mundus the concept of Revolution, or [blank] isn't good enough, so destroy it. This is the moment where the idea was born.

Suddenly having Meridia and her Aurorans as antagonists in Knights of the Nine makes a whole lot more sense in the grand scheme of things.

So Mehrunes is Meridia's brother (sort of)?

The same could be said of any Prince and often is. Why would Meridia exile from the Stars that made Dagon?