First of, he needs to address what he and/or his partner are putting out into the universe that no one wants to deal with them, and to the extent that their children suffer.
Secondly, he needs to be reaching out to their biological grandparents and extended family with the guilt trip. Yes, the kids are innocent. But it is their family that is taking a personal issue with him and/or his partner out on the kids.
1st off... He stumbled upon the information. Secondly, they shouldn't be lying and cutting school to avoid a test that everyone else has to take. And their parents shouldn't be condoning that behavior.