Using multiple monitors and a switch with Surface 4

Hello. I have a Surface 4 laptop, and I have two monitors plugged into a dongle that is connected to the laptop. I have a third monitor that I would like to use, but my understanding is that the Surface 4 will only support two monitors at a time. 

If I get an HDMI switch box and plug two of the three monitors into it, can I switch back and forth between the monitors and have it still count as only two monitors? Additionally, I would like to have two of the monitors mirror each other. 

Basically, I want to have one monitor show what is on the laptop screen, and two monitors mirror each other. 

I am slightly tech-deficient, so please talk to me like I'm a super-smart 5th grader. Thanks!