You all will be playing in the same modded infested dumpster fire that Rockstar games are on PC.

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Why don’t you try it and see? You launch the game through R* and your friends launch the game on Steam. Then try to invite them to your posse.

That being said, it’s not a guarantee that both you and your friends would be on the same server if all of you were to use Steam or Rockstar’s launcher.
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