Looks cool, might try it out after an update or two. How much "sandbox" are we talking about? Something similar to "Confined With Goddesses", more, or less.
And this is just a personal nitpick/suggestion. The femboy brother looks to have breasts in the previews. Personally if their was an option to corrupt them more to fem and make them a dickgirl (encouraging taking hormones perhaps?) I'd be all for that, I believe the current art gives a false impression in regards to that character at least.
I do want to iterate, the femboy is fine (i mean, I am into dickgirls, so femboys are just a step from that.) Just wanted to let you know. (also, I was serious about the whole dickgirl thing, having an option to influence him into that path would rock.)
Edit: Is pregnancy planned at all? for even an ending?