IMO the reverse vesting is unjustified. You typically see it after raising a round, as a way for investors to protect against founders immediately leaving a newly funded company with shares that have "real" value now. Bringing on your CEO isn't that kind of event; the reverse vesting only protects the new CEO, and he's not putting in a real investment up front (an investor is putting in $X dollars today; your new CEO is building equity over time like you guys).
You and your technical cofounder should be compensated in equity for the two years' work you put in. If you get pushed out of the company before your cliff, you will have nothing to show for your efforts. I'd really fight for two years' vested stock up front.