Yup, that's the correct form we use. Biggest issue I see on rental properties is borrowers not claiming taxes and insurance, or not claiming HOA dues which negatively impacts their qualifying income we can allow. The lease agreement is only really useful if property is a recent acquisition/recent conversion to rental and not on taxes. Otherwise, tax returns are preferred as that is a record of what the property actually generated.
Regarding your wife's part time income: I don't see how they'd have a problem with that given she has over a 2 year history in the same line of work with the same employer, unless her w2s and YTD gross pay reflect wide swings in income. If her paycheck reflects YTD gross I can figure a year to date average. You give me w2's and a start date I can figure a long term average of what she has earned since she started. I will look at previous w2's to see the monthly average for both years as well and compare that to YTD. If w2's and year to date reflect year over year increase, we're golden. If YTD is over 10% decline from previous, I will ask for documentation/explanation as to why(receives a year end bonus, ect). With income, the way I work is generally start with the most conservative calculation and see where that puts my Housing and Debt to Income ratios. If it's approvable, fine, move on, if not, I will look at other income(any Bonus, OT, Incentives, ect) and potentially using different calculation for base pay. The main issue is if comparing 2015 w2 average to 2016 w2 average to YTD monthly average there is a year over year decline, at that point, it's hard to justify using any of her income.
What gets confusing when trying to explain mortgage underwriting to people is depending on who the loan is being sold to(Fannie/Freddie), there are different guidelines/document requirements, and individual lenders have their own overlays depending on the companies risk tolerance(so lender A may want X doc, but lender B does not, but it wants Y doc instead). Then, individual Underwriters have varying risk tolerances that impact how they look at documents and income. The guidelines may tell the UW what they need, but it's up to them to interpret them and apply that to the documents.