two lesbian twin sisters who are both 25 years old who are in an incestuous relationship with each other is morally okay in my opinion because what they’re doing is completely harmless.
Just because society thinks it’s gross and weird that doesn’t mean that it’s morally wrong.
I feel the same about gay incest.
The only thing wrong with incest (assuming both parties consent) is inbreeding. If there’s no chance of inbreeding, and there’s no grooming/coersion/rape, what’s the harm?