I haven’t tried it, but the mavproxy docs reckon you should be able to set multiple masters.
I went looking and found this PR where that was introduced, including updates to all the files that make use of the autopilot symlink. It seems like the /dev/autopilot simlink setup is done when companion is installed (either using setup.sh or updated with post-update.sh), by moving the relevant udev rules to where udev can find them.
It may be helpful to specify the exact usb locations, as was done in this post. I believe you should be able to find them with ls /dev/serial/by-id, or possibly lsusb.