My requirement is household income of at least 3x rent.

See bestplaces.net to see what the median household income and average rents are.  

Except as detailed in this consent, the SoFi personal loan may be used for legal, personal, family or household purposes."

I am looking to hire my 7yo son as a household employee.

That market is so incredibly saturated I would suspect that every single household in King County has received at least one yellow letter in the past 3 years. 

We share childcare and household duties 50:50. 

For example, if my gross household income is $100K/year and we invested $10k in starting Airbnb, can we take this deduction from our personal taxes?

You can also take a look at your net worth return on investment which also includes loan pay down and equity growth.Also, make sure to look at the municipality's max occupancy for unrelated individuals in the household.  

Income: What’s the median household income?

Of course, I could be totally missing costs/expenses that you may have that may not be common in my markets.Just curious for context, what is average household income (in USD)?