Here’s my approach. Bear in mind that it covers the basic needs you’ve described but could be easily expanded into more robust solution. Few steps to follow (all code goes to your functions.php):

1. Save company name as user meta

The first thing we need to do is assigning a company name to a user – i’d go with user meta to achieve that. You could add a metabox to edit user screen for easy management, I’m not including code for that here, but I’m sure you get the idea.

For testing you can just add meta to user with update_user_meta( $user_id, 'company', 'Tyrell Corporation' ); (codex)

So in this example I assume that we have a bunch of authors with Tyrell Corporation set as company user meta key and editor with exactly same meta.

2. Add Company meta to posts based on author’s user meta

To make things easier and cheaper, I’d keep the reference to Company name also in every post saved by any author with company assigned (that way we can get rid of at least one query to author meta table every time we’re checking editor’s rights to edit the post later on). To do that, I’m using save_post hook:

function save_company_meta( $post_id, $post, $update ) {
    // get author's company meta
    $company = get_user_meta( $post->post_author, 'company', true );

    if ( ! empty( $author_id ) ) {
        // add meta data to the post
        update_post_meta( $post_id, 'company', true );
    }
}

add_action( 'save_post', 'save_company_meta', 10, 3 );

Now every time a user saves his/her draft, the company name that was assigned to this user is copied to post meta.

3. Map editor’s edit_post capability

Finally we can simply map editor’s ‘edit_post’ capability. If the post’s company meta data is different than editor’s company user meta, we take the capability to edit this particular post away from that particular editor. There are some additional conditions in the code below, for example we don’t apply restrictions if the post has no company meta at all or is not a post post type. You can align that to your needs:

function restrict_access_to_company_posts( $caps, $cap, $user_id, $args ) {

    /*
    We're messing with capabilities only if 'edit_post' 
    is currently checked and the current user has editor role
    but is not the administrator
    */

    if ( ! in_array( $cap, [ 'edit_post' ], true ) ) {
        return $caps;
    }

    if ( ! user_can( $user_id, 'editor' ) || user_can( $user_id, 'administrator' ) ) {
        return $caps;
    }

    /*
    $args[0] holds post ID. $args var is a bit enigmatic, it contains
    different stuff depending on the context and there's almost 
    no documentation on that, you've got to trust me on this one :)
    Anyways, if no post ID is set, we bail out and return default capabilities
    */
    if ( empty( $args[0] ) ) {
        return $caps;
    }

    /*
    You can also make sure that you're restricting access 
    to posts only and not pages or other post types
    */
    if ( 'post' !== get_post_type( $args[0] ) ) {
        return $caps;
    }

    $post_company   = get_post_meta( $args[0], 'company', true );
    $editor_company = get_user_meta( $user_id, 'company', true );

    /*
    if no meta data is set or editor is assigned 
    to the same company as the post, we allow normal editing
    */
    if ( empty( $post_company ) || $post_company === $editor_company ) {
        return $caps;
    }

    // finally, in all other cases, we restrict access to this post
    $caps = [ 'do_not_allow' ];

    return $caps;
}

This wouldn’t hide the posts completely from admin UI, you can still see them on the list, but editor cannot get into post’s edit screen and change it nor see the draft (WordPress will automatically remove all “edit” links for you, also in admin bar on front-end).
Once the post is published, the Editor still wouldn’t be able to edit posts content.

4. (Optionaly) Remove posts from admin list completely

If above still isn’t enough, you can also hook into pre_get_posts (codex) to hide posts from admin list completely:

function query_company_posts_only( $query ) {

    if ( ! is_admin() || empty( get_current_user_id() ) ) {
        return $query;
    }

    $editor_company = get_user_meta( get_current_user_id(), 'company', true );

    if ( empty( $editor_company ) ) {
        return $query;
    }

    $query->set( 'meta_key', 'company' );
    $query->set( 'meta_value', $editor_company );
}

add_action( 'pre_get_posts', 'query_company_posts_only', 10, 1 );

Hope that does the trick, just play around with it and add some improvements here and there.