Hi,
I’ve created a plugin that shows how to do it – maybe it’s already sufficient for what you want to do:
https://github.com/itthinx/groups-sandbox
Please download the repository’s zip file and install it Plugins > Add New …
Now you can use the shortcode [groups_sandbox_posts] to embed a list of posts on any page. The shortcode takes several attributes which are documented in the plugin’s readme.txt – you’ll also see it on https://github.com/itthinx/groups-sandbox
Here are some example usages based on your questions:
Can I make a list of blog posts that contains only posts for members of Group A? Another one for Group B? And another one for Group C?
[groups_sandbox_posts group="A"]
[groups_sandbox_posts group="B"]
[groups_sandbox_posts group="C"]
Also, can I make for example a list of blog posts with posts just for Group A and C?
[groups_sandbox_posts group="A,C"]
If you don’t provide the attribute suppress_filters="yes"
the above will only render post links for visitors who are allowed to access those restricted posts.
At some point we might add such a shortcode to the core Groups plugin but I suppose that this will help you, you can of course customize it to your needs …