did you buy them from the same breeder, you buyed the previous birds?? i think he has some serious worm problem in his loft. i have seen this sort of poops with heavily infested birds. but as they are new, this poops can also be due to stress of shifting to new home. wait for a few days until they get used to the surrounding.
however deworming should be done twice a year to keep your birds worm free.