I think this is a terrible idea. I definitely believe in the one founder mentality. There needs to be one person who drives the vision, and a team to execute on it.
If I was going to have two co-founders, I wouldn't consider offering the other founders more than a 52% / 24% / 24% split, with one person clearly defined as the leader (be it me or one of the other founders) and driver of the vision.
If you aren't comfortable with that from a voting standpoint, simply require all important votes (sale of company, transfer of equity, dilution) to require a supermajority vote. Lawyers have standard language that clearly define these kinds of scenarios.
But 1/3 1/3 1/3 is just asking for trouble on minor details down the road when one person needs to clearly be in charge.