ILR Set M - Dependent Child Question

Hi,

This may seem a very straightforward question but I am confused. So my wife and stepson are now applying for ILR after completing 5 years on spouse and dependent visa. I have completed the section for my wife and now completing the section for my step son. There is question asking who is are the parents or legal guardians. The options I get are my wife, me (as I am her husband and sponsor and put my details in during her part of the application) and someone else.

The information state’s biological parents, step parents and any legal guardians. My wife has sole custody of her son form her first marriage. If I select my wife and me then it does not ask about my step son’s biological father at all.

Please advice.