if one parent has a gene visible, the offspring has a 100% chance of at least carrying the gene.
in the case of breeding a feather wing vis parent with a demon wing car parent, there is a 50% chance of the offspring carrying the feather wing gene (but not showing) and a 50% chance of the offspring displaying feather wings (while carrying the demon wing gene).

it's sort of like, where N = nothing, A = feather wing and B = demon wing,
assuming the feather wing vis parent has the genes AA, while the demon wing carrying parent has the genes NB,
the offspring can be NA (carrying feather) or AB(displaying feather but carrying demon)

however if the feather wing vis parent has the genes AB instead (displaying feather but carrying demon), and it breeds with a demon wing carry parent, the offspring would have a 25% chance of carrying the feather wing gene (NA), 25% chance of carrying the demon wing gene(NB), 25% chance of displaying feather wings (AB) and 25% chance of displaying demon wings (BB).

wow that was needlessly complicated.

Thanks for the help. I think I get it now.

Also since it has been told that i can't breed siblings, does that mean I can't breed father-daughter or mother-son or some such?

I am assuming that is a no.

Yea you can't breed parent and child. However if you found a mate for one of the children and breed them the children could breed with the parents I believe. Basically Grandparent and Grandchild is okay I think. XD If I'm wrong someone correct me.

I'm hoping thats right or my breeding project wont work.(Maybe know is a good time to use my essence, but...)