You'll find out a little more about Peter in the sequel and prequel (prequel has quite a few chapters, but none elaborate on how he turns yet). I may include more in the published version of NOHW, which I hope will release on Amazon sometime this year. For now, just know that everyone has a breaking point, some thing that you can use to manipulate them, and the Association found his.
The monsters do it for money, for power, for so many reasons. It just depends on the person. Again, this will be discussed more in length in the published version and in the sequel.
As for May.... Well, I'll let you draw your own conclusions. The prequel (Scars on Her Back) may or may not hint one way or the other.
Hope this helped. ☺️