For a 40 year old woman, who lets them to kiss her and touch her and make her cum and gives HJ, they are no more children. Sophia herself admits that she sees Dylan as a man now and not only his son, she is Sam's secret girlfriend, not to play along with him but because she enjoys Sam's antics and fooling around with him. A person who has crossed the line has crossed the lines, moral and ethics make no sense for them, so if L&P blue balls Sam and Dylan but rush the progress with DeShawn, it just means that more people want to see Sam and Dylan's path but he is not ready for it and thus compensating with DeShawn. Regarding Sophia eating out Ellie, it's all natural progression. Sophia already made out with her near the pool, and masturbated her in the shower so it is only logical that Sophia eats her pussy next, can't argue there.