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Pretty simple question
Who are the primarchs and did any of them join horus in the war. Also are any still alive and what are their stories.

The sons of the Emperor. Some are still alive. Some joined Horus.

http://wh40k.lexicanum.com/wiki/Primarch

A quick search of the forum will tell you everything you need to know, there's at least 47 threads started about them each week. I'm pretty sure there's a sticky all about them at the top of the forum too. Google could also be good.