Using a Macbook Pro as a second monitor for another Macbook Pro

My parents are visiting us for Christmas, and we'd like to watch a movie together. We have two Macbook Pros between 4 people and no TV or other display, so we'd like to watch the same movie, synchronised, on both computers. We're on the same WiFi network but don't have any HDMI cables, thunderbolt cables, etc.

Is there a way that we can use one of the Macs as an external monitor for the other Mac, in order to achieve this?

Unfortunately, the Bluetooth antenna is broken on one of the machines, so a Bluetooth solution won't work for me. However, feel free to post one in case it's helpful for other users.

so we'd like to watch the same movie, synchronised, on both computers.

You can leverage the Screen Sharing feature built into macOS to achieve this. You'd just need a network connection (which you happen to have via Wi-Fi) and would NOT need any cables whatsoever.

To use Screen Sharing, on the MacBook on which you'll be playing the movie, go to System Preferences app → Sharing and enable Screen Sharing.

Once configured, the other Macs in the same Wi-Fi network would be able to see the configured MacBook and can request access to your configured MacBook.

However, in this scenario, you'd have to resort to using the original Macs speaker. So the audio playback would only be from one MacBook (which would also be the case in an external display scenario).