Let's define names, then.   Two people mutually stand and claim to support the other for the rest of their lives, share their values, share their property, share their name, be known as an indivisible couple, raise their children (natural or adopted) responsibly and care for each other as best they can.

As far as I can see this is a marriage.

If they're both named Nancy , it changeth nothing about the substance of the deal.

A