What should a person do with their Marans that end up having too dark of eyes? ...are they useful for anything in a Marans breeding program
I presume you are referring to Coppers? It should not be difficult to get the correct eye colour if the birds have the correct,Birchen ER, 'e' allele.
Two...
This line is know for looking like production red birds and having webbed feet and blue legs.
This sounds like they have a mixed genotype, and two bad faults. OK for producing dark eggs, but as Marans, no way.