You can click on the Video link below to see how to book multi-city ticket.
​Departure flight Oct 12 
SEA-ADB 
and return flight
Oct 21
IST-SEA  

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SEATS:

Below  is a link to the Seat Guru layout of the seats on the SEA-IST  and IST-SEA flight

If you click on a seat it gives you the description.  They are also color coded to denote green a really good choice to orange being a warning.

https://www.seatguru.com/airlines/Turkish_Airlines/Turkish_Airlines_Boeing_787-9.php