Family Member of an EEA National visa application

Hi guys,

I help my parents to filling up application form for visa in the UK. And we really need your advice please.
My mother non-citizen of Latvia she needs a visa to come to the UK but she is going to travel with husband (my father) He is citizen of Latvia and he doesn't need a visa. So if they are travelling together my mother can apply for Family Member of an EEA National Visa which is free instead of General Tourist - 6 months visa which cost about £90.

Iv'e got couple of questions regarding filling EEA National section. Does this section for EEA Nationals who live in UK only? Because one of the question is : What is the EEA National Registration Certificate number for the EEA National?
My father never been in UK before. He don't have this certificate.
Also they ask National Insurance number and UK address. All those questions are mandatory.

Do you have any thoughts? Are they able to get this type of visa or they need to pay for General General Tourist visa?

Thank you.

FP can be used by persons moving with sponsor to UK (as well as to join a sponsor already based in UK) so UK-related details are not expected in all cases.