is this a normal moult?

Yes it's perfectly normal at this time of year.  Older birds moult heavier and earlier than younger birds.  Also poorer layers tend to moult earlier.

Birds lose their feathers in a set pattern as you have observed they don't tend to moult evenly.

I'd just focus on ensuring they get regular layers pellets as their staple diet, a handful of mixed corn at night and not too many treats.  Some people like to feed a bit more protein once moult is fully underway and new feathers have started to appear as whit quills.  Feathers are mainly protein.  Soya or tuna in water (not oil) can be given in an evening 2 or three times a week.

Some people change to growers pellets rather than layers as they think that extra calcium isn't needed while they aren't laying but I wouldn't do this.   During moult your birds are renewing their calcium stocks in medullary bone which they will need for their new laying cycle.  The rest during moult is an important period of renewal and good nutrition is important during this time.  I wouldn't start to experiment with supplements other than maybe adding a multivit to their water.

Best of luck
HF