Venom, Solid, Solidus, Liquid, and Naked Snake are all different people. Naked becomes Big Boss. Solid, Solidus, Liquid are clones of Big Boss. Venom thinks he's Big Boss. I don't understand what's so confusing? :)
Kojima may be a genius game designer, but he's an awful writer IMO. None of his lore makes sense, and is only convoluted for it be served in exposition dumps in hour-long cutscenes. Death Stranding is a prime example of that. I enjoyed playing it, but can't remember a thing about the motivation of any of the characters.
Not quite, because they were not all direct clones the way we think of cloning in real life, because in the Metal Gear universe, they could do "selective cloning".
I forgot the details of how exactly they described it (and I haven't played beyond MGS3 yet). But in MGS, Liquid and Solid have a conversation about it, where Liquid insinuates that they took the "best genes" of Big Boss to clone Solid (who actually looks like Big Boss), and used the remaining "weak genes" to clone Liquid. I would bet that this whole explanation is also sprinkled with a bit of nanomachines-related lore in the later games.
Also, their differences in looks could be explained by environmental factors and style choices. I would argue that Solidus looks just like Big Boss and Solid, but aged, more muscular, and with different facial hair.
Revolver Ocelot: "Yes. The inferior one was the winner after all. ...That's right. Until the very end, Liquid thought he was the inferior one."
Inbefore someone says "it is an old game", I beat MGS 1+2 just a couple years ago for the first time ever, and I usually am more into newer games. Still looking forward to play MGS3 and the rest of the series in the future.