ACL issues

[NautilusIII]

Hi!

I have some trouble with access-control for my categories and albums.

I have some albums A,B,C and D.
I have users U1,U2, U3 and U4, and a Group G1 where U1 and U2 are part of.

I want U1 and U2 (and noone else!) being able to view A; this is easy by saying "Album can be viewed by members of G1"
I want U2 (and only U2!) being able to view B; do I need to create a group for this user only - that causes a mess when too many users are used!
I want U3 (and only U3) being able to view C; same issue as before.
I want some unregistered users be able to view D using a password only, but then the ACL assignment changes to "Can be viewed by me only", but I want U1, U2, u3 and U4 to see this album too, although it has been created by U1 only.

How can these issues be solved?

Thanks.