Well, you are likely going to have a continuous problem if parents are not on the same page, unfortunately. If he does not nap at home and is only with you part-time, you MAY be able to get him to nap, but it will take some time and hard work at his age. I always ask about napping at the interview to avoid this type of family. If they are not napping at home, I don't take them. Too much headache! As it stands now, all you can do is be firm and keep putting him back to bed until he realizes he isn't going to get out of it. Good luck!