TK's website, and app are pretty unreliable. I tend to have more luck using their app to do seat selection for a partner award, but when the aircraft changes, they won't automatically assign people on the same itin to adjacent seats. So, assuming you still have a couple months out, it is worth periodically checking in every month or so before the flight in case of an aircraft change so you can select the seats you want.
Additionally, if you try to select seats too far in advanced, the seat map might not even be up to date. e.g. we were booked for a short haul domestic within Turkey on business, but it was showing 3x3 layout even starting from row 1. Then a few months later after a schedule change, they finally updated their seat map to the correct 2x2 layout in Business