Can I buy a fourplex or not?

[Jeremy Bates]

Credit score: 700-ish
Salary: 75K plus $15,000 from another rental property
I can have 20 to 26,000 in the bank for reserves but would also need to use it for the down payment (3.5%) if that's legal, to use it for both.
I've got about 25,000 line of credit and have about half of that in debt I'm repaying. Two student loans, at about $20,000 total.
No car loan. No boat debt, dumb debt, etc.
Here's the problem: my tax returns from the last two years don't reflect my current salary, not by a long shot (25K-ish). I've got a cosigner with stellar credit (750+) but with him signing, he doesn't have assets/healthy salary to back up the score. NINA possibly, but I do now have the income.

If I can buy a fourplex in the DC area, %1,700-$2,400 in rent per unti per month, can I just take a higher interest rate for my tax return and cosignor issues?