Equity split – Looking for seasoned advice

So I've been building out my startup for 2 years now and have decided to pivot into a new idea that is a lot more promising and has signs of traction. My current situation is as follows, I own 51% my co-founder owns 49%, however, I can buy back all of his 49% shares for a nominal price if he doesn't hit a few milestones by the end of the year. It doesn't look like he's going to hit them.

The tricky part is, we're bringing in a CTO/technical co-founder for 25% and because of my other co-founder and I's agreement, he's suggesting that we form a new corporation for the new idea, and structure it 37.5%, 37.5%, 25%.

So he'll be getting his full 37.5% ownership in this case, where as in the other case he would be out if he didn't hit the milestones, which seemed to be heading in that direction.. Do I stick with the original agreement, or form this new company so we can get the CTO in?

Can we get the CTO in the original corporation, even with the original agreement in place?

Please advise!