Show in admin UI only children

Why not make two separate post types: ‘company’ and ’employee’

Can’t I query in my admin box only child pages (eg depth: -1) ? The entire site custom coding is laid on that format

You can alter the query used by the metabox using the ‘p2p_connectable_args’ filter:

https://github.com/scribu/wp-posts-to-posts/wiki/Admin-box-filters

Thank you for your fast and prompt response,
honestly I don’t know how I could use that filter

What function is there used to echo the results in the admin box?

Perhaps, if that it’s way out of reach, is it possible to put a conditional somewhere (even if needs entering into plugins code), for example to display a specific post only if custom-field[‘test’]==1, or anything I could wrap arround