Of course, you've already read through some of this thread from the top of the Egglaying forum:
https://www.backyardchickens.com/t/423023/why-arent-my-chickens-laying-here-are-your-answers
They are past the transition time and really should be laying eggs if you and your boyfriend have been waiting 4 weeks.
Urg.
Since your other hens are laying, this is a real puzzler.
Are there windows in your coop so that light from dawn and twilight gets in the coop. Laying is all about lighting. With the days getting longer, they should be laying. If you don't have windows in your coop, then you need to let the hens out at dawn. You probably have windows, but I've seen coops with no windows and think, "Ooops ... made by someone who doesn't understand chickens."
How about the protein level of the feed? 16% protein is like the lowest diet most hens can manage to lay eggs on. Because protein costs so much, 16% is what most commercial complete feeds contain. However, there used to be some 18% protein layer feeds out there. Maybe you could try that.
Along the same line, maybe you could limit their feed to just their complete balanced laying feed ... assuming you sometimes give them table scraps or scratch. Of course, keep providing the animal protein-rich table scraps (milk, meat, cheese, pan scraping, bones from the roast to pick clean). The grains (corn, oats, etc.) are lower in protein than the complete layer feed and lessen that 16% protein level, which is necessary for most chickens to lay eggs ... so extra grains are not a good idea until after they get re-established laying.
The old stand-by: Keep fresh water available at all times. Eggs are made up of a lot of water. (I'm sure you already know this!)
I don't know ... I'd guess something like maybe they weren't laying for the old owner, but that's not true because you were getting eggs from the new hens when they arrived at your place.
Color me stumped. I suspect you know all this, but I don't want you to think no one is paying attention.