If you are able to participate in KOE then you'll be able to intermarry with other families. Similarly, after Exposition begins you'll be able to intermarry. However, I seriously doubt there will be any effort made to provide functionality for this prior to KOE.

Marriage.

You can't simply go out and write something saying, we are brothers now, but the process of marriage and child birth allows you to pick the surnames that are kept or given up. Either spouse can take the others last name, or keep their own.

You could technically be related via surnames still, you just have to figure out the specifics based on the actual scenario. For you and the mayor to be cousins for example, there would have to be a marriage regarding one of your aunts, or uncles, or some such.

I understand where yall are coming from but i was just asking considering you can simply go out and say ok we are having a child and its in a contract form. Wondering if Surname Family links wouldve been the same but i understand thanks guys.

You can't sign a contract to gain the benefits of a family bond, case in point would be wards, which can take up a new surname but don't get the family benefit just from taking a surname.

There was mention around last March of a cadet family line feature. It was mentioned in relation to the Persona project. We have not heard much about it since then. I mention it to point out that SBS are considering extensions of the family system.

I actually really like the concept of linked families and it would help deal with many uncomfortable or confusing scenarios for launchies.