A single form submission, either from the Forms JS API or the REST API Submit Form endpoint, will only ever update one person record. This cannot be changed.
As Darshil mentions, there are various heuristics that determine which record be updated, but again it's only ever one record.
In addition to the above, the default lookup key for a form post is the Email Address field in the absence of other information. It's possible to add an additional field as a lookup key, but you won't be able to use the system SFDC Type in this way. (People typically use fields like Company or a custom Account ID, although having a compound lookup key can itself be dangerous and/or confusing.)
When we need to "spread" the effects of a form submission across other people, we use a webhook-powered service. The service loops back using the REST API to get all people matching, most commonly, the Email Address of the person who fired the 'hook. Then it writes field values from that person onto other people in the set of matches, applying any other kind of logic along the way.