I don't know if these have been confirmed or not, but my questions about harem are:
1. Does the "harem" mean actual multiple relationship acknowledged by every character involved (e.g.: Mom/Jo/Nat ok with sharing MC)? Or does it simply mean you can have sexual relationship with multiple characters individually (e.g.: no group sex content)?
2. If it is the first definition (harem = group sex), are all characters harem-able? We can assume Mom/Jo/Nat, Jo/Twins, Twins/Marsha as safe assumptions, but how about other characters that don't really seem to fall into any "group" yet like Abby, Eveline, Samantha, etc?
Probably far too early to ask these questions, but just looking for any confirmed answers about this topic if there's already one.
As much as a "harem" is acknowledged by all and entered into freely by the MC's partners it is worth taking a look at the notion of "free will" when it comes to this.
As you have already surmised Marsha and the twins are not against sharing. Samantha has the same stance and so does Jo. Nat' stance is a bit muddy and Mary is not even close to being on board with something like that. Abby is a strictly one-girl-one-guy kind of girl, so how to get them into the harem?
By using your energies and influencing them. Is this free will? No, but if you want some of the women to be a part of the harem, that is the only way of getting them there to begin with. If they are inherintly against such things, you need to keep up the influence.
Some might even change their stance on the matter once they are in the fold, but far from all.
Groupsex is a big yes! But given the amount of women available and therefore sheer number of combinations down the road, I think I'll be asking my supporters who they would like to see engaged in group activities in certain updates, based on predefined selections made by me.
This is not yet a thing but it may be down the line as the harem builds up its members.
I hope this answers the question to some extent. Writing this on a phone is a hassle!
Cheers - Kaffekop