I highly recommend that you look at the actual, day-by-day historical weather statistics for the last five years or so on timeanddate.com, and check all three cities. That data will give you an idea of the range of weather you can expect. Even much farther south in the Balkans, it can turn raw in October.
I've linked to Warsaw's stats for October 2018. Do be sure to check multiple years.
For what's it worth, on this year's trip elsehwere in Europe I learned the virtues of mostly-nylon slacks that proved to be relatively rain-resistant, though definitely not entirely waterproof. Merino-wool long johns underneath kept me comfy even on a couple of wet, 40ish (F) days.