How to share posts in WordPress Multisite?

It’s the first time I am using the multisite option. I must be searching for the wrong terms, because I can’t find the answer to what I think it’s a simple problem…

I have 3 sites.

1. Group Landing site
2. Group 1 site
3. Group 2 site

Essentially, Group 1 and Group 2 will have separate contents. However the Group Landing site will have content from both. I would rather not have the user enter the content twice. Using Multisite, is there a way for me to poll content from Group 1 and Group 2, and display it in Group Landing?

If not, what’s a better option to share content between sites?

You could use the function switch_to_blog

Example:

switch_to_blog( $site_id );
$post = get_post( $post_id );
restore_current_blog();

It should do exactly what you need. After switching you can use a custom query to get the relevant information