Income-rent ratio multiple tenants. Combine or separate?? (WA US)

[Jason Schlieger]

I want to apply a 2.5x or 3x requirement (my rental price is 2000 on a 3bd sfh for reference). But i'm not sure if this should be combined for multiple unmarried) tenants? I would appreciate your thoughts on a few hypothetical ideas.

If its one person, a 3x ratio suffices. But i was thinking, mathematically, if its 2 tenants who combined make 3x then its less risk; because if one loses their job its about half the income lost, not all of it. So technically wouldn't it be preferable to have 2 tenants who meet income ratio combined but have multiple sources of income?

Basically, i feel like if i would allow one tenant at 3x, it would be super ridiculous to say that one tenant who makes 3x cannot apply with someone whose income is 1x instead of also 3x.

Is it legal to say i want to increase income-to-rent ratio for more tenants such as "one tenant needs 3x income, two tenants need 4x income combined"? Or another wording like "one tenant needs 3x income, two tenants need 2x income individually"?

Or how about two or three tenants together are fine but the wording is "at least one tenant makes 3x"? Legal and non-discriminatory?

Thanks!