I really don't want my one friend to be left out all the time I play story missions or me being left out if the other 3 come online before I do.
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It's called play in groups of two and switch out 3 is fine there's no need for more then that. 6 is for raids so you guys can raid all you want together. If it's that big of an issue for you the wait for the division but pretty sure that's 3 squad only with a companion app as the 4th.