They might be a bit stressed from the introduction of the newbies, as things that happen today can still affect the egg production a fortnight later (like if they go without water for a day, for example).

You could try giving them a bit of Poultry spice on their feed, which would perk them up whether the problem is stress or the moult.

But do make sure no one is being bullied, and that none of the birds have got red mite (you'll need to check every nook and cranny of the house too), as the weather conditions have been perfect for a red mite population explosion.

Best of luck!