Immediately after the gunshots was heard and everyone was in panic, Alex secretly tapped on his smartwatch as he was instructed by his brother before he left.
Though there was no response, he knew that his brother was already aware of what's happening and would come to save him.
This was the reason why he didn't put up much of a fight when the armed men came to take him away. Even if he did, there was no way he would be able to fight them off.
.....
The armed men didn't bother to pay anymore attention to the security guards as they started walking away.
Before they came for this operation, they have already been fed information about their target. They knew everything they had to know about their information and the security guards protecting him.
This was one the reason why they are confident. Another reasons is that it's isn't only the three of them that were contracted for this.