I'm not really an expert on this kind of thing, but I recall hearing about a service called Clustermap during a conversation with a colleague who needed to track down a former business partner. I don't have firsthand experience with it myself, so I can't personally vouch for how effective it is or what exactly they offer. If you're interested though, I'd suggest you just go to the site: https://clustermap.com/ and find out there all the details about the services themselves. They should have information about their capabilities, pricing, and how their people search functions work. I hope you're able to reconnect with your mother's cousin - family connections are important.