You just answered your own question....You upset the pecking order and caused some stress...In due time they will start laying again. Nothing to worry about. Put some ACV. In their water for a few days. They will be fine.
Yep. Chickens will stop laying for three main reasons: stress, lack of daylight, or they are simply too old. In your case, it is stress. They'll be okay and will start laying again soon. What you can do is just make sure no one is being picked on too badly and ensure that there are two feeding and watering stations to cut down on stress. This will let the "old" flock eat and drink in one place and the "new" in another which will make life easier for both sets of chickens. Hope it works out!
How much space do you have for these 25 birds?
How did you introduce them?
If you live in a hot area, skip the ACV.
Do you free range? They may be laying out in range area.
Free range birds sometimes need to be 'trained'(or re-trained) to lay in the coop nests, especially new layers. Leaving them locked in the coop for 3-4 days can help 'home' them to lay in the coop nests. Fake eggs/golf balls in the nests can help 'show' them were to lay. They can be confined to coop 24/7 for a few days to a week, or confine them at least until mid to late afternoon. You help them create a new habit and they will usually stick with it. ..at least for a good while, then repeat as necessary.