I think if you and your friends worked together, but now, some amount of time has passed then, it should be fair enough.
Whether anybody is a) going to bother, and b) going to prevail - those are the important questions. (And note, even if the chances of b are vanishingly small, you most likely don't want a to happen if "anybody" includes large well funded organisations with practically unlimited legal budgets... I would not poach ex cow orkers from say, picking a random example, Oracle - unless it was _very_ clear I was permitted to do so.)
*Cautionary note, this won't actually stop a litigious former employer or jackass lawyer from filing a lawsuit. > https://hbr.org/2017/06/the-uber-waymo-lawsuit-it-should-be-...