Hi, Skier,
Fellow Scrivener user here. Welcome to the forums.
A) The reference you make to ‘up to n family users’ is about the license for the software, meaning you can install the software on several computers within your family. This has nothing particularly to do with collaboration, which is what I think you are talking about. The original poster here was also not talking about collaborative writing, but just wanted to set up and give a copy of a project to someone. I am guessing you have in mind more of a two-way street.
B) Scrivener is an exciting and amazing writing tool (I am not affiliated with L&L), and I think it will do great things for your project. Still, collaborative writing can be a complicated prospect, depending on how much integration you are looking for. ((There is perhaps some ambiguity as to whether you are trying to share between you a particular document from within a given project or the whole project. And when you say “share” do you just mean “send a copy to” or do you mean “actively hold in common”?))
There are various strategies for collaborative writing out there, but each comes with its complications and caveats.
Here is one example of a way (which Lunk was pointing to): One can use Dropbox for full-project collaboration, but doing so safely requires discipline and care on the part of each collaborator. You can share a Dropbox folder between the two of your macs — anything placed in that folder on your mac will sync with Dropbox and with the corresponding folder on your partner’s computer. So, a Scrivener project placed in such a folder will automatically be synced to both computers. But here is the big caveat with this set up: You cannot literally work on this project simultaneously. If one person has the project open on their computer, the other person must not have their copy open on theirs. If you are careful and coordinate with your partner and always remember to let Dropbox have time to sync before opening the project, and also to always close the project and let it sync at the end of your session, you can work this way pretty seamlessly — but there is an obvious danger in it.
There are other strategies depending on what you are meaning to do which range from simply Exporting a single document so as to send a copy to your collaborator and then importing an updated version when you get it back. There is a Sync-with-Folder function which will do roughly this same thing with every document in the project. Etcetera.
If you are just starting out (with your project and/or with Scrivener), I suggest you find the simplest and safest way that works for the two of you and use that. Later on, with more experience of your needs, you might experiment with some more elaborate techniques.
D) When it comes to collaborative writing you might want to go to the tips & techniques area of the forum and search for ‘collaboration’ and its cognates.
best,
gr
P.S. The mention of Dropbox in particular by me and Lunk, as opposed to any other such service, is not an accident. Many such services are not safe to keep live Scrivener projects on, because they do not handle project “packages” correctly and this can lead to the corruption of your project — even if you are not collaborating with anyone. Dropbox is approved by L&L for use with Scrivener. In fact, it is the only sync service that the iOS version of Scrivener will accept for syncing back to your laptop.