Stress & egg laying

I'd be grateful for advice.

I have five chickens which currently all sleep in the same coup but are in separate halves of the pen during the day as the oldies still do not like the new ones (we are only in week two).  We swap ends every day as one end just has a shelter whilst the other has the coup.

The new ones are yet to lay which is fine however the oldies are only laying when they are in the 'coup end' but that said today they were there and we had no eggs.  Typical when we were about to collect them for pickling!

I wonder if this is stress?  They are only about six months old and have always laid very well.  Also, how long does it take an egg to form inside them as I don't get it how they only lay when they are at that end.

Any ideas?

We have been told the oldies are Rangers.  They are typical brown hens.  Two have laid every single day even when it snowed.  There is no trace of any eggs so I don't think they have and whilst the run is great it's not so big that we couldn't see an egg.
I just hope they are ok.  I do worry about them and you regularly put my mind at rest!

Your advice has been priceless in the past.  If I lived near I'd regularly provide you with wine!

sorry to interrupt your lovely chat!
is there any way that you can separate the ru nso that they both have access to both the shelter and the coop? (eg different entrances to the coop)
or can you get a nest box somewhere in the area where there is no coop?

when we got our newbies we had a completely separate coop for them and then
 (e-v-e-n-t-u-a-l-l-y) put them all in one coop at night.
but that was after they'd been doing the free-ranging together thing for ages first.
(separate runs inside the main run but together-ish when out in the garden)