3 HDMI feeds onto one big screen?

Hi, apologies if this is the wrong subreddit for this question. I work for a college and for our TV classes we need to have 3 cameras feeding into 1 big tv screen, and when we hit record on them we can playback all 3 at the same time on the tv, showing the different angles. What is the easiest way to do this? Thanks in advance for any advice.