The cases for your parents are two separate petitions. You (the petitioner) are filing a separate I-864 for each parent. Your household member (not joint sponsor) will need to file a separate I-864a for each parent.
Your household size is 5 on all the AOS forms. There is no place to count intending immigrants on other affidavit of support in your household count. This mean you don't count mom on the I-864 and I-864a on the AOS forms for dad, and vice versa.
