help to sex sussex/Faverolle chickes

[Silkie fluff butts]

We decided to let our broody hen hatch chicks for the first time (for us and her!). We don't know much , but are reading up on things. The rooster is a pretty chill, handsome Salmon Faverolle and we have very nice and happy Salmon Faverolle and Sussex hens. Is the Faverolle gene that produces the color change at 3 weeks dominant or recessive? How and when will I know if they are roosters? I want to sell most of the chicks, but I'm not sure of the best way to handle this and what to tell people who are interested in buying them. Also, The 7 eggs were laid over a weeks time. Will the mama keep sitting until the last one hatches, or should I get an incubator? We have candled the eggs and all are developing nicely so far. Any advice is welcomed!