I am developing an embedded solution using C and I am working with two USB sensors. If I connect each sensor alone they take this names:
Device 1 (I do not know why it takes 6 names...)
You should try using the names in
/dev/serial/by-id instead, since those names include the name of the device and should not depend on the order of connection.
By the way, it is also possible to write udev rules that make symbolic links for the serial ports depending on what device they belong to. I am not sure how that would work for a composite device with 6 serial ports, but there probably is a way to make it work.