I'm not sure what the nutritional value of the feed your using is, but it's probably fairly decent. We're very spoiled here in the U.S. and not used to breaking down the value of individual grains to make a mix of our own. The commercial mixes we commonly use have some very specific percentages of proteins, carbohydrates, amino acids, vitamins and minerals. This doesn't mean that hens can't lay perfectly well on other feed, they've done it for centuries after all!
I'm looking for some info here on BYC and on the internet as a whole for some things that are in layer rations that may not be in a mixed fowl feed like your using. Really though, I have to think that 'mixed fowl' means just that!
Possibly they could use a little more protein and calcium than is in your mix. Your hen's combs and wattles seem a little pale, this could be a sign of age, or a sign that they are going through a molt, or are low on some vitamin(s).
I know this isn't helping you immediately, but I'm looking for some info for you and I'll bet others are too!
//edit// I'm sorry I forgot to say,
and also that aside from they're not laying very well, your hens look very nice! I hope we can help you get they laying better so they don't have to go to the soup pot just yet!