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You can always use ssh if it is enabled on the RasPi, no matter if the RasPi is connected to a TV or not. How to enable ssh look at SSH (Secure Shell) and SSH using Linux or Mac OS. If you want to have a full graphical user interface with windows you can use VNC. How to do it look at VNC (Virtual Network Computing).
2
Issue the two command as superuser
systemctl enable ssh.service
systemctl start ssh.service
1
How simultaneously do you need it to be? If "within a couple of seconds" is fine, then just call your scripts sequentially via SSH:
sshpass -p 'raspberry' ssh pi@192.168.0.2 python take_photo.py &
sshpass -p 'raspberry' ssh pi@192.168.0.3 python take_photo.py &
You may want to setup a passwordless login to make the commands simpler.
If you need to ...
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