Connect both headphones via bluetooth. Both should say connected on the Bluetooth setting page.
In Finder menu hit Go -> Utilities -> Audio Midi Setup
You should see both your headphones listed on the left here.
Hit the “+” button at the bottom left and select “Create Multi-Output Device” (You may rename the device if you wish)
Select your bose headphones from the list on the right to add to the Multi-Output Device.
Right-click on the Multi-Output Device you just created and use device for sound output and play alerts and sound through this device.
You may also select which device as your master device to sync across all your connected headphones.
I also selected Drift Correction for slave devices - I’m not 100% sure what this does but I think it makes sure that your devices stay in sync to the audio/video playing on your computer.
Watch away. Note that you won’t be able to adjust ouput volume from Macbook any more, instead volume is adjusted individually at each headphone, which is pretty neat.