When you’re in a FaceTime Group call, you might have noticed that FaceTime will automatically enlarge the window of whoever is speaking. If you are having a chat with 4 or more people, the other windows can resize and move around during the call, which can be distracting and confusing. For those who prefer to keep everyone at the same window size during a call, Apple has released a quick method that is available on the latest versions of iOS, iPadOS & MacBook.

FaceTime on iPhone

Whilst these instructions are primarily for iPhone, the process for the iPad should be quite similar. Please ensure that your device is running iOS 13.5 (for iPhone) or iPadOS 13.5. If your not sure please see below.

Open settings.
Go to “General.”
Tap “Software Update.”
If an update is available, you’ll see it here. If not, your device will tell you it’s up to date.

Now that your software’s up to date, here’s how you can stop FaceTime windows from resizing.

Open settings.
Scroll down and tap FaceTime.
Navigate to “Automatic Prominence.”
Toggle off “Speaking.”

FaceTime for Macbook

First, make sure your Mac is running the latest MACOS (currently Catalina 10.15.5)

Click on the apple icon, located in the left corner of the menu bar
Select “System Preferences > click on “Software Update”.
You’ll see what macOS you’re on and if any updates are available here.

To change your FaceTime preferences:

Open up FaceTime.
Click on “FaceTime” in the left side of the menu (top of the screen)
Select “Preferences”
In the pop-up window, under “Automatic Prominence,” uncheck the box next to “Speaking.”

Source: https://www.theverge.com/21271103/facetime-resizing-windows-iphone-ipad-mac-video-group-call