I voted Marans cross just for the olive egg potential of offspring. If you can tell what eggs are from whom then I'd go for the crosses that produce most eggs. Likely that's your Red and Rock then the Marans eggs just for the color potential. My reds always gave a reddish brown egg, Rocks a light brown/tan. Those higher producers and the dark Marans cross would provide a colorful basket crossed with the EE Cock.
By the way, your red looks like a sex link which is a hybrid not a RIR.