Hi @Kristina_Bobrowski, welcome to the Asana Community Forum!
You can collaborate with clients, contractors, customers, or anyone else who does not have an email address at an approved Organization email domain (i.e. @gmail.com or @yahoo.com). These people would become Organization Guest 
1. Can Subcontractor A see Project B if they are not invited to Project B and are not invited to the Team that Project B lives under?
Guests have limited access to the Organization and only see what is explicitly shared with them.
- If you share a task with them; they will only see that task.
- If you share a project with them; they will see that project and all tasks within that project.
- If you invite them to a Team; they will see all public projects within that Team, providing they’ve been added as a team member.
If two people are seeing each other as a “Private User”, they are both Guests. If Guests see this, that means they are not working in either the same team or project together; this is to ensure that if you’re working with clients, they cannot see one another’s names unless you want them to. Once they are both working in the same project or team, their names will be displayed for one another.
In order for Guests to see one another’s names, they must be Members of at least one project together. Just add both Guests as Members to the same project and they will then be able to see each other’s names.
2. Using that same scenario, can I see Subcontractor A’s calendar view across all projects I’ve added them to or can I only do that if they are a Team Member? And if I can, how do I do that?
You can search by the contractor name in the search bar to access their My Tasks list. Then you can access their Calendar tab. If you need to manage their my tasks, you can request access.
I also recommend you checking this great post from @Bastien_Siebman: Who sees whom, a guide to guest visibility with Batman & Robin
I hope this helps!