What are some tools to help analyze domains to investigate possible scams?

A relative was scammed and I'm trying to dispute the charges.

I see that whois.com will provide some information such as:
https://www.whois.com/whois/texags.com

The registration dates of several sites involved are all very recent and do not indicate established businesses. Two of the domains send emails directing you to a supposedly legitimate business with highly inflated prices. How can I show a connection between the sites or collusion?

Is there anything you can glean from common name servers or Registrant contacts or are those common?

I'll crosspost to Outdoors for their input.

Whoxy.com will give you the registration history and allow you to look for other domains that had the same registrants. Is that what you're asking?

I guess the history helps some, but if the registrant is GoDaddy.com, that doesn't narrow it down much.

I was hoping for some way to find other domains with the same owner.

Another common tactic of scammers is to buy expired domains that have a legit history, They'll even leave the contact information set to the previous owner.