That chart for sure includes higher portion of double income households (because now more women are in the workforce than in the 80s). This reconciles your view with the Fed graph
Households can have more than two incomes - roommates, children who work, grandparents etc.
In practice, household sizes have gone down over time as more people live on their own, which means the income graph is lower than it otherwise would be.
As for dual income families, they're mostly a good thing that happens when women can afford to pay for childcare. That is, that book The Two-Income Trap was mostly false. This is part of the topic of Claudia Goldin's economics Nobel, the other part being that the gender wage gap is caused by motherhood interrupting women's careers.
(Edit-misspelled Fed)