How to have a business show up when an associated business is searched for?

My client is a doctor who owns a few businesses which provide tangentially related services that aren't directly tied to his practice. The services are also medical and apply directly to his discipline.

I've been asked to make it so that when you Google his name, his businesses show up on the first search page, beneath the search results for his clinic. His clinic, and the two businesses all have different domains.

What steps can I take to make this happen? The business website mentions his name on several pages, and his clinic's website links to the business we want to appear in the search results. Do I need to simply increase the amount that the name of his business is mentioned/linked and vice versa? Thanks.