There shouldn't be any tax consequences for the founders if you've made 83b elections--the election meant you paid tax already on the full value of the stock at the time of the election (presumably zero) even though it was subject to future forfeiture. If you sell newly-issued stock there should be no tax impact. If you sell your own common stock, you'd pay tax on the gain, but I doubt that is what you mean here.

Of course, you should not take the free advice dispensed on Clarity and consult your own tax preparer--this is not tax advice.