I see some crazy people here, who are not willing to take a chance to shit on Ryker by making his sister part your harem. I command your restraint, but I cannot follow such methods. You must not forget the mc is a kind person, who can melt the hearts of any women. So by showing that to her, you'll bring her to your side making any plans Ryker has fall short.
I'm just having fun, but I really don't see Ryker using his sister in any meaningful way. Mainly due to the reason Jamie sent you on your quest, which was to help the women around and make their life better by being around. But I also have a problem in harem games, and I find it hard to refuse women unless I really don't like their personally or looks. I like seeing the chaos and the attempts an harem prog try to go through to please a giant group of women which is hot but I can't help but laugh at the same time(I mean it's just crazy).