Yooper, I might see a few errors in your thinking.

These are single-phase 'whole house' water heaters. I assume that means that these will each be going in a different residence, and different panels.

Does the load seem high? Sure - that's the price you pay for 'instant' heat.

When you do the load calcs for multiple dwellings, there's a multiplier for your "diversity factor." The effect of this is, whether you use the 125% figure or not in each individual panel, I don't think it will change the final total service needed.

Looks like you need 3 two-pole breakers - and they;ll need to be mounted next to each other, so they can be considered as disconnects 'grouped together.'