Thanks NoSauce That article is interesting but it actually focuses on separating a child (or rat in this case) from the mother from the "point where the babies begin to recognise their mother's face and voice" separation can then cause "traumatic emotional responses".
I'm paraphrasing but the researcher is essentially studying the affects of completely cutting offspring off from the mother and not substituting the mother. Homer himself argues that the emotional response was largely due to a loss of warmth a child receives through bodily contact, nutrients and psychological interactions with it's mother.
You could argue that the two dads are the mother figure in this scenario, they bonded from birth and are providing the warmth, nurture and psychological interactions their children need to prevent them being traumatised.
That cannot be compared to a baby or rat being isolated postnatally.