The thing that you are going to do is really interesting for me. However, you are right. The Raspberry Pi has only one camera port. It means that you are able to plug only one camera module. Although, you can connect any normal USB camera to this board.
fosa USB Camera for Raspberry Pi can be a good option for you. It needs no driver and it's easy to use ...
What is a line follower robot?
Line follower or Line detector is an autonomous robot that follows either black line in white are or white line in the black area. The robot must be able to detect a particular line and keep following it. You can implement it by camera or IR.
As you specify, you want to do it by camera. In this case, you have a lot of options....
The "Camera" port on the Raspberry is not a DSI (which stands for Display Serial Interface), but a CSI (Camera Serial Interface). While similar, they are electrically different and cannot be used instead of each other:
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 firstname.lastname@example.org python take_photo.py &
sshpass -p 'raspberry' ssh email@example.com python take_photo.py &
You may want to setup a passwordless login to make the commands simpler.
If you need to ...
Apparently the problem is noise on the PIR power line triggering the PIR. This can be caused by virtually any other device, even the MCU doing something. I have the same problem caused by the MCU going into sleep mode. Some suggest filters on the power line, some get away with delaying re-arming of the PIR until nothing else is happening which could cause a ...
The options you list are only available for a customized version of motion called MMAL Motion which accesses the Raspberry Pi camera directly rather than through /dev/video0. A wiki for that version is here.