Need help with date array

I have three date fields. They can range from all being null to all being populated with date of birth values.

I want to create three formulas: youngest DOB, second youngest DOB, and third youngest DOB.

I'd appreciate any help coding these.

Requirements: if the result for any of these formulas will be empty, I need to know what "value" will be in it, so I can test for this elsewhere in my report.

Thanks.