The federal fair housing act prohibits discrimination on the basis of gender and familial status. “Familial status” excludes unmarried couples and it is still illegal for unmarried couples to live together in many states. It is unclear if denying a single unmarried person is covered by federal law. Probably not. However, under New york, New Jersey, Maryland and Massachusetts law it is quite clear that the behavior you’ve articulated is illegal and may be the basis of a civil lawsuit.
As a side note, my dream tenant would be single and financially stable. Furthermore, no laws require disclosure of these things or prevent subletting.
You can rent the apartment and then sublet or assign to your divorced relative without secular legal problems (unless otherwise specifically agreed with landlord).
Disclaimer: I am posting this anonymously with no representation that this post was made by a lawyer, and it should not be relied on as legal advice.