When you say control "at the same time", are you contemplating that all tvs will be showing the same content simultaneously

Here are a few problems...so far...

#1. Vizio is not a commercial TV. It may not have the ability to be turned ON or OFF via discrete commands. It may have a POWER button that toggles between on and off.

Why is this bad? What if 1 TV doesn't turn on when it should? Pressing the POWER button will then turn off every TV and turn that one on. They will be out of sync.

If you have not purchased TVs yet please get something else.

#2. You need a control system that will let you send commands from a centralized location out to each TV to turn it on/off and possibly set its input.

#3. You need to distribute your video source via HDMI to each TV from a centralized location. There are multiple ways to do this with different types of wire and products.

#4. You need to be able to control your content. I assume you dont want to pay a person to sit there clicking "next" "next" on a slide show. You will need hardware or software to do this.

#5. You need to plan the system up front so that you know what wire to take to each TV. 1 Cat5 to each TV = you wanting to kill yourself or someone wanting to kill you.

The question was asked about digital signage hardware since most manufactures of that hardware have thought about how to control the TV along with outputing the content.

I looked up the TV he has listed and it is a 42" smart TV w built in apps. I think he is trying to have each TV internally play content from a networked location like you would in your house. You have 2 options unless the TV supports IP control, walk around to each TV with the factory remote or spend the money on a routable control system w your choice of user interface. Whether that is pc based, tablet (ipad) based or handheld remote control based. Any type of solution will cost anywhere from the price of one or two of those TVs to doubling the cost of the overall project.

+1

If all will show same content, HDMI splitter (if only 1 source) may be the easiest way.
Again, way too many unknowns to answer this properly.
 

The pro he hires will definitely help him work this out.