1. I understand the confusion. MLO is not really a scheduling app-- you have to think of it more like a To Do list, when you can set dates on things. People who are heavily calendar-oriented (like myself) need to keep track of things as they relate to time in general. For example, if MLO outline isn't organized by time (and whose would be?!), I might have two subtasks next to each other, where one happens Monday and one happens on Friday. They may be together because they're logically part of, say, the same project, but if there are other things happening on Monday that are elsewhere in my outline, I do not see them in MLO that way.
By pairing with the calendar, I can have the events appear according to their dates and times which, for any person guided by when things happen, makes it clear what's happening when.
Even so, you're beginning to brush up against the paradox between two ways of managing time, but that's probably the subject for a book.
2. There are several ways to arrange this, and I have worked on them extensively.
Firstly, understand that MLO, like any application (both mobile app, and desktop) is document-oriented. This means that when you open the application, you also open up a document-- in this case, the document is a particular tree with its body of tasks.
The synchronization lets you synchronize either a chosen document, or even just a selected branch within a document.
In my own case, to keep from having to switch between documents when I am working with others, I prefer to add the shared tasks to a branch within my tree, and then share only that branch of shared tasks. Another approach would be to have a personal file, and then a shared file, and the other person only has access to the shared file. None of this is secure, however, and any person with a login to your cloud (necessary for them to sync with) could sync any of your files they so choose.
And since MLO doesn't have any sort of roles attached to its tasks, you must create them using tags, or other indicators, so you know who owns what.
You will probably find older discussions (some from me, possibly) about how to do tags (historically, they're "Contexts"-- but we've often overloaded them for many other purposes-- now that tags exist, which I haven't played with, this could change). My Context system is very complex, so I have categories of them, which I designate with things like @loc_ for locations, or @who_ for people, or @tim_ for my time management stuff.
As far as licensing, they'd just need a copy of whichever MLO app they're going to use, and access to your cloud.