For a dog not to be eating properly there is more than likely a medical or a behavioural issue such as stress as the reason.Food means a great deal more to dogs than we give it credit for, it means survival to the dog, so for them not to be eating I would A) consider a visit to the vets after a few days settling in and B) consider whether the dog is stressed or anxious.
They should be considered first before chopping and changing foods as the constant change can have a detrimental effect on the dogs stomach and intestines.
Dont watch the dog eat as your stress can have an effect on the dog, dont force them to eat however dont leave the food down for them, give them 5 minutes and if they leave it pick it up. Dogs, in full health, will not starve themselves so if they are not eating rule out the two above before changing foods.
