How big is your water heater? 4 of those with a regular shower head can drain the tank pretty quickly.

It will be tankless. This is the one I'm talking about.

Here is a link that might be useful: Kohler Watertile

It's a rain head. There is no real pressure to the delivery by design. It flows gently, not massages. That's what rain heads do. If you want force, you don't want a rain head. You want a body jet.

And having a tankless is no guarantee that you'll have enough hot water for one of those multi outlet showers. You've got to calculate the incoming water temp and the maximum rise to see the maximum amount of hot water that is able to be produced. Most tankless don't operate well with high demand showers. They just ask for too much hot water from anything but a commercial boiler.