I was feeding the adults on chicken scratch mix. Plus in their living area there is a lot of vegetation: different grasses, seeds, vegetable plants that they help themselves to. They also eat bugs, worms, frogs etc that they dig up in the enclosure. I think that the parents got most of their nutrition from theirsurroundings; They certainly didnt seem hungry in that they would spend long periods of the day just resting, and would never follow me around wanting food as the two chickens I also had in there did. Before I put the adult guineas into the enclosure they used to roam freely around my property and were given minimal feed, only at the end of the day to encourage them not to stray.
Perhaps there wasnt enough suitable feed around for the chicks. THey seemed very helpless, but I thought that they would start eating in the same way my quail chicks started eating (and survived).
They may have been full given the food around them (hence them not chasing you for food), but it's possible they didn't have a lot of energy. I don't really know the behaviour patterns of Guinea Fowl, but extended periods of resting doesn't seem overly normal to me, perhaps it's a bit of lethargy? If the food they were consuming wasn't providing them with enough nutrients and energy, yet keeping them full, that might explain the poor hatch results.
Chicken scratch mix is not designed as a complete diet, merely something to throw out as a treat for them to scratch around and eat. I'm guessing there aren't enough bugs and the like in their enclosure to provide them with enough protein. Generally it's suggested that before breeding, poultry be put on a quality breeder feed for at least 6 weeks before incubating eggs. I'd be inclined to think you'd want to do much the same for Guineas.
I would be putting them on something like Showbird MP and then see how things go. I think you're likely to have more success.
To rule out any environmental issues, you could try grabbing some eggs as they are right now and incubating them in an incubator. If you have the same problem with the chicks raised in a brooder, then I think it would let you know for sure it's a nutritional issue with the parent birds.