Family resemblance does not make two children’s needs interchangeable.

Looking alike, sharing a house and a surname, laughing at the same jokes tells you very little about what each child needs. A routine built for one can fail the other quietly, because the mismatch reads as difficulty rather than difference. The resemblance is what makes the error easy, since it seems reasonable that what worked before will work again. Each of them is asking for something specific and probably not saying so directly.

Take a routine you apply to everyone in your household and ask who it actually fits. Adjusting it for one person is not favouritism, it is noticing that they are a different person.