How to refer to people and how they're related?

Question

I'm trying to document an issue with an application, and I'd like to refer to the people using different words regardless of the relationship (father, son, etc.) being used.

To better explain the issue, see the following:

A. Carl is the father of Oscar.
B. Fred is the son of Martin.

I'd like to refer to A's Carl and B's Fred using the same word. I would think that they are the subject of the sentence, but is there a different word?

Also, A's Oscar and B's Martin should also have a word that refers to them. Are they the object of the sentence, or is there another word?

Answer 1

Subject is usable and correct. Its first sense in wiktionary is

(grammar) In a clause: the word or word group (usually a noun phrase) that is dealt with. In active clauses with verbs denoting an action, the subject and the actor are usually the same.

However, if you are “documenting an issue with an application”, unless grammar details are the issue, some other term may serve better. If Oscar and Martin in your examples are persons who filed applications or are subjects of applications, there might be confusion due to use of the term multiple ways. You might instead use one of actor, agent, applicant, application-filer, party of the first part, etc. For the names appearing in your examples as objects of preposition of, perhaps the phrase their relative would work.

Answer 2

Carl and Fred are the subjects of their sentences. I wouldn't use any other term, nor do I think there is one.

Oscar and Martin are prepositional objects.