All the 'wait until next week' advice does NOT apply to such tiny hatchlings. It's very important to get them feeding within 2 weeks of bringing them home (or sooner, depending on their condition), or assisting is necessary.
I wait 2 to 3 days between feeding attempts with small ones. Assist-feeding has had a good track record for me--done properly, it can get most hatchlings eating on their own after one or two assist-feeds. Never force feed, and always be aware of how delicate the babies are--avoid breaking teeth, or using too much pressure which may tear the throat lining when you put the pinky rat in the back of their mouth.
I do send hatchlings out after 3 feedings, but I feed my hatchlings rapid-fire, every other day or every 3 days, when I start them--so they're bulky.You would be absolutely amazed by how fast they grow on this schedule. I believe it's better to feed hatchlings up as often as they'll eat for the first month or two, to get some bulk on them so they can withstand stresses and short fasting periods.
It's possible the hatchlings you bought DID eat multiple meals with no problem. But, what were they eating, and how often? In a brand new place, how much reserve did they have to draw on while they get used to it?