Rest API, relationships and subsets - rest

Question

I have some questions about Rest API and relationships.
I know the questions of relationship is always tricky with Rest.
I have some users, posts (created by user), relationships between users (imported from fb), interactions on posts (created by user) and users can like a post.
User can create a posts which will be seen only by others users who have a relationship (up to 2 jump, like friends of friends) with the poster and then can create interactions on the post.
We do a filtering on the backend based on your authentification and just do the magic on /posts which will return you the list of post that you can see.
It feel a bit funky to me because it make the same endpoint (/posts) will return different set of data based on the current user. We could of course pass a parameters (?viewable_by_user_id=:id) to reflect it a bit more, but I wonder if I can do anything to improving caching.
I'm thinking of improving our API to a v2 with this endpoints:
GET/PATCH/DELETE /users/:id
POST [post] /posts: create a post (using current auth user as the owner of the post)
or
POST [post] /users/:id/posts: create a post for this user
GET /users/:id/posts : get posts created by the user
GET /users/:id/stream : get posts "viewable" by the user (this is the one I'm strugeling with)
or
GET /posts?viewable_by_user=:id
GET /users/:id/like : get posts liked by the user
POST [post_id] /users/:id/like : like a post
POST [interaction] /posts/:id/interactions : create an interaction on the post for the current user
GET /posts/:id/interactions : get post's interactions
GET/PATCH/DELETE /interactions/:id
Any thoughts on how I could make the path reflect a bit more the relationship?
I've thinking on creating an endpoint for relationships but seem a bit to complex to maintain (users don't create relationship manually, we pull them from fb)
Thank you for any feedback, and let me know if my question is too ambiguous or irrelevant.

Answer 1

What if you think of it as this: (Note that I just like putting "posts" first since it tells what and then the restrictions go to the right of that. You may like the other order.)
GET /users/posts/<viewer>/<creator>
This gives some degenerate cases:
GET /users/posts/<me>/<me>
to get all the posts I have created
GET /users/posts/<me>
to get all the post from all other users
GET /users/posts/<me>/<stranger>
would return nothing because I am not allowed to see the stranger's posts
GET /users/posts/<me>/<friend>
would return the posts from my friend.
NOTE: In all cases, all posts returned are those allowed to be seen