I have never seen this picture. Think you can find it and post it here?
Even without the picture, instinct would instantly kick in and they would try to go for air. A single wrap of tape isn’t going to hold that or hold them together for long. They had to be taped together with several wraps. Each wrap decreases the chance of it being a suicide.
It does not sound like suicide, it sounds like honor killing.
Two sisters committing suicide? They won’t choose drowning, pills maybe, gunshot maybe, but they are not gonna tape themselves together and jump in a river. I don’t care what race or culture they are from, it won’t happen.