Collaborating on a Project limiting viewers

I just recently joined a team and they are working on a sensitive project in Storyline. They've already built a lot of the content that will eventually be used to train the entire company. The only thing left to do is add scenario based quizzes, a few images to accompany the content text slides and audio over the content text slides. Due to the sensitive nature of the training we don't really want anyone else to see the content until it is totally completed. To share the project between collaborators it seems like the easiest way to do this is using the "Team Slides" feature in Storyline. Then I can edit/add and the other 2 people on my team can do the same. However, it seems that if we add it to "Team Slides" anyone at the company with access to Storyline could potentially see the project as it's still evolving. Is that correct? Is there anyway to limit the number of people that can see the project? Is there a way for 2 people to be in the Storyline project at the same time?

Also, I was looking at Rise as a potentially alternative solution. It seems that is a good place to create courses and collaborate but may not do the job we want it to do. Basically we a trying to create a course that will play about 15 minutes of content followed by a brief quiz with scenario based questions. The learner could only advance to the next section if they pass the quiz. I think I would need to build that all in Storyline so Rise wouldn't be a good option for this?