Yes, I may have no knowledge of award availability with ET (as ET does not appear when I search for availability and secondly, ET would not be my choice of carrier) but great that apparently it is not difficult to get to DUB with ET, but the OP needs to get to IST! DUB-IST with TK is of course an option (if seats are available) but it will not be on a B787 (most likely on a B737 or A321)

The reality is that the OP will face scarce award availability and will not be in a position to be able to choose between multiple carriers. If the OP is prepared to go with ET to DUB, then fine by me, but this will not be what the OP wish for.