Taking your father's application first...
There are two questions...
When the 'Yes' button is clicked, the programme jumps to a pop-up that asks for the children's details. This question is intended to capture ALL of the applicant's dependent children. This helps the ECO understand the applicant's family ties.
The next question is looking for the the applicant's 'Non Dependent Children'. This is intended to capture adults who are travelling with the applicant. Your father's application would fill out this section, including the pop-up.
Eyes wide. Astute observers will notice that the two questions are neither mutually exclusive nor collectively exhaustive); it can get tricky and there's a need to be a little bit careful. The ambiguity is built-in by design.
For your application...
This is where you would list your father's details because he is your sponsor.
For both applications...
There's a question about who is travelling with applicant...
Both applications should select 'Yes' and fill out the associated pop-up. The pop-up does not ask for the other person's GWF number, also built-in ambiguity. So "best practices" is to use the remarks section to link everyone's GWF numbers together so they can tell it's a family group application.