1. Correct your wife should be your primary sponsor regardless. Now... the joint sponsor does not have to be a direct or indirect relative. It can be just a friend too. As long as they meet the poverty limits and are permant residents of US.
2. Her aunt needs to put 1 (herself) and 1 more (you). Total = 2.
3. Yes, it should be 1 (your wife) and 1 (yourself). Total = 2.
4. Correct. Use any supporting documents that come from valid sources, such as taxation papers, SSI, employment letters, etc. (Don't use I-130... that is for K2 and K3 visas. You are a K1? Correct? If you are K1 visa, then use I-864!)
Mister Jones reacted to Detron in K-1 Visa AOS Affidavit of Support Joint Sponsor HELP Needed (i-864)!