Is this a one-way or a two-way street? Two-way with an equal but as a parent one-way if they are slackers. Don't be OCD for minor infractions.
IMO, when the kids do not want to help and are actually trying to find ways to get out of the work, they are not following your principle, they are not giving the respect to their father that he gives them. Right On Cobra.
As a group-home worker with 8 boys 13 to 19 years of age, some of the guys worked harder to get out of work than it would have taken to do the job right. some guys damaged things when asked/made to do chores.
If that means he has to enforce those rules by getting on to his kids, even getting angry, is he the wrong person for getting upset or are the kids wrong for not respecting their father enough to help willingly? Enforce the rules w/o belittling and nit picking.
