Worldtraveler222

Not a problem 

Why is his birth certificate take that long? , it is easy to get and you get it same day at the Oficialia in DR. all you need is a pdf form and print , you dont need original to send with the i-485. Some family member can get the birth certificate and scan and send it to you by email or whassapp

You'll also save a lot of money by filling before the fees increase.

Intention was determined at POE, so no issue with him entering and 'changing his mind' after the fact.

Are you adjusting status or are you going through the consulate? 
The consulate is more forgiving with past income and present income but generally USCIS is more strict.
If going through consulate you should be fine. If adjusting status, I would prepare for an RFE for joint sponsor. 

While his I-94 is unexpired he has lawful status. The second the I-94 expires he moves to unlawful presence and is deportable, but once you file I-485 (in your case it would be concurrent filing of I-130 and I-485) and the filing has been accepted by USCIS he moves to being in a period of authorized stay and unlawful presence is no longer accrued. The I-797 is his proof of authorized stay at that point. Since he's in an immigration gray zone at that point he needs Advance Parole to be able to leave and reenter the US at that point until AOS is approved.
 
Note that you will face questions at the interview about adjusting from B2 since it is illegal to enter on B2 with the intention to AOS.

Your "current income" is how you qualify.  For the "employed" current income does not come from a tax return.  In that section state your current income from your job.  Calculate it as your gross for a pay period, times the number of pay periods in a full year, ie: every two weeks is 26.  Document the current income with a copy of that same pay stub.
 
You will get a case not saying your income doesn't qualify and you MAY want to use a joint sponsor, BUT "the Consular Officer will decide...."
 
Just ignore that message.

~~Moved to AOS from Work, Student and Tourist Visas- from AOS Family K1/K3- as the OP 's spouse entered as a tourist/B2.~~