wheaten is coming from RIR, but Birchen is Dominant over wheaten so the chicks will grow to be much like their goldend cuckoo maran parents, with some gold leaking on the breast, their rate of lay will be right in the middle of the Marans and RIR..
I dont think the "Lemon Cuckoo" pattern exist in the Maran breed(would not be hard to breed) as in Lemon cukcoo orps(use goole o see pics) but I think you may refer to whats called, Golden cuckoo maran, while golden and lemon may describe a similar color, the pattern names have totally different...