People who say ‘My names are…’ think they know simple grammar than most of us because when two to three names are mentioned, they assume that’s a plural noun phrase.
For the ones who would listen, let’s tell them this: a full name is a singular nominal concept because it refers to one individual and represents a singular object.
Whether you have one or ten first names before your surname, they refer to YOU. They all combine to form your identity.
- My name is Mirabel Spencer.
- My name is Brian Advik Kofi Mohammed Angelo Ademola.
However, the plural form might make sense if you answer different names in different places (e.g. as a secret agent), though this is an unlikely situation.
- My names are Michael, Zlatan, and Luiz.
Bonus: a surname is also known as family name, last name or second name (British).