when we draw the trend line drawn in the two points should they coincide in price?

They may or may not coincide depends on the situation. You get the neckline by joining the peaks of two shoulders.

As you can see in the image there was a small setback, I don't know if it counts as a definitive setback

Yes, it is correct, sometimes price might test back the neckline levels, you place trade after a strong candle breakout of neckline level.

I hope this clarifies your doubts. Feel free to ask if there is any doubt.

Thank You !!!!