1. Read the materials and links I provided.
2. Review the applications forms and guidance
3. Make an attempt to complete the forms and note the documentary evidence you have to support your answers
By doing that you'll have a much better idea of what information is needed and just what documents you have already and what documents need to be obtained.
Your EEA National sponsor needs to write a supporting letter indicating how you qualify as extended dependent.
You'll need to move fairly quickly as if you leave it too long after your EEA National sponsor arrived to UK your case of dependency will get weaker.
Good luck