A hen can store the roosters genetic material for a little over a month after mating. With only 2 pullets to 2 cockerels, I doubt you'll see many infertile eggs. You are more likely to see bald backed hens from over-mating. I highly suggest getting more hens, or rehoming the roosters. The hens could become injured and stressed. Stressed hens do not lay as well.
Back to the topic at hand, fertilized eggs do not taste any different and do not have any nutritional difference.There is no embryo in the egg until it is incubated.