Gmail and multiple tags if multiple person use one account. Like in a company

Also a new memo from me to me:
To use gmail better, it is good practice to make tags/titles for mails, also group them with directory tag.
To move new mails to multiple tags, make a filter that pins tags one-by-one with filter-by-filter. So you need to make multiple filters also. To apply tags for old mails, just search them, and apply tags from the dropdown.