In the end, Kay decided that the best person to make the final call would be Kyle.
In her opinion, Lianne should be told the whole truth as she would not warm up to other people easily. Finding out that such a person was only there for a job (even if they did form a real friendship later on) would be more detrimental than good.
Also, Lianne was unique and observant, thus, would benefit more from the guidance that is more structured. She's observant and straightforward, so she should be cultivated better.
As for Joseph, he was slightly dense, so he would most likely not be told the full truth. Most definitely, he could not know about the existence of MIB but having someone beside him for protection should be okay.
Kay smiled a bit.
It wasn't that Joseph was dense, but rather, he was really like a clean slate.