Aso&Pusa

In this case, I think the only way to get all the income on the joint tax return counted is for you to add both parents to your I-864 and have both of them  do an I-864a. 
 
 

You are overthinking this.  He is reporting income he did not receive 1099s for. Unless somebody pays you more than $600 as a contract employee during the year they do not have to issue a 1099.  I report income I have received for services from various clients on my Schedule C. As an example--If you made birdhouses and sold them at craft shows you wouldn't get 1099s, but you are supposed to report the income and expense of your birdhouse business on Sch C.
 
 

Ahh....I see. You need to combine because he doesn't qualify by himself. In that case you are going to have to either provide really good documentation of his separate income (all $23,500) because his tax return does not show what is Mom's and what is Dad's. You know she earns nothing, but the immigration dudes need documentation on paper. Normally an employer letter  and pay stubs work, but not for him. 
 
So the interest income...if it is from a joint bank account or investment, then it's not all his. Gather everything that has only his name on it and add it up. I guarantee there is a 1099 for everything...interest, dividends, IRA distributions, Social Security retirement, pensions. You mention misc income. If you mean he gets paid cash for odd jobs or something, that doesn't count for this because he is not reporting that income maybe (?).  So find every 1099 that has Dad's name only on it, add it up, and use that number as his income. Then maybe make a list of those items stating --The separate income of John Smith is as follows. Kinda point out you are including his documented separate income. And follow that with photocopies of the documents.  It ain't gonna be easy to pull this off without an RFE.

Have you thought about a simpler way to do this?
 
YOU
I-864
tax return transcript
 
DAD
I-864 (list Mom as his household member because of the joint return doesn't show separate)
joint tax return transcript (avoids finding/photocopying all those 1099s) optional 2 more
Proof of citizenship (required of joint)
MOM
I-864a 
 
 
 
 

He receives 1099's of his income. You don't file 1099's because the IRS gets this information electronically.  However the 1099's are an integral part of his return records.
And if submitting paper copies of the return to support the affidavit then copies of the 1099s are needed to be included in the documents

It depends on what their tax return shows. I understand its a joint return but it still shows who made which percentage of the income. SO if the joint return shows income of 20k and 15 of it was attributed to your father and 5 to your mother to use the 15 from dad he fills out an 864a. to use the 5 from mom she fills out the 864a.
 
In some cases even where "Dad" is the only one with income on the joint tax return they still like to see an 864a from mom showing that she is aware of what Dad is doing. So I would recommend sending one 864a from each of them with their respective part of income from the joint tax return on it.