Here is a summary of choices you have to make to achieve all 16 endings.

Aryan Dies
Iorveth Path - Stennis killed.
Iorveth Path - Stennis spared.
Iorveth, Triss Path - Stennis killed.
Iorveth, Triss Path - Stennis spared.
Roche Path->Henselt killed.
Roche Path - Henselt spared.
Roche, Triss Path - Henselt killed.
Roche, Triss Path - Henselt spared.

Aryan Lives
Iorveth Path - Stennis killed.
Iorveth Path - Stennis spared.
Iorveth, Triss Path - Stennis killed.
Iorveth, Triss Path - Stennis spared.
Roche Path->Henselt killed.
Roche Path - Henselt spared.
Roche, Triss Path - Henselt killed.
Roche, Triss Path - Henselt spared.