"Can I come inside?"
Kain made an offer, but was actually testing the limits of these people.
Although it was unknown what kind of relationship these four people had with each other, Kain temporarily grouped them into a common group, because they were all suffering from the same condition.
Kain's question was, on the one hand, to confirm the status of this person, or these people.
If the person standing at the door agreed to let him in, but the others did not, then it proved that they could not be grouped into a common target group, and needed Li Qing to separate them to target.
If this person refused to let him in, then there were two possibilities. First, these four people were different from each other, so they would make different decisions, if that was the case then Kain would just need to try again next time with someone else. Second, all four of these people refused to let him in, if this were the case, Kain would have to change his approach.
