No, I don't think that is disrespectful. It was a practical consequence of Mia's highly unusual choices in life: to keep on adopting children, and adopting, and adopting, for 25 years in total.
To the point where a girl from the other side of the world, born to different parents, sold to a rich white couple, transported to and raised in New York, in an unstable 'family' where adoptive children received unequal treatment compared to biological children, had become a distant 'sister' to another adoptive child 15 years younger, and to a cuckold child 17 years younger - two children who have NEVER said anything sympathetic to, or about their 'sister' in 33 years.
Had MIa *truly* wished for all her children to have, and maintain a healthy, durable sibling relationship, she should have made *very* different choices regarding them.
In fact, Mia *poisoned* her children's relationships; humiliating, physically and mentally abusing Soon-Yi, kicking her & kicking her out of her house and her life; and never forgiving her for loving the man Mia had already dumped four years before.
It would have certainly feasible for Moses, Dylan and Ronan to understand the situation. They knew full well that none of Mia's 'Previn children' from her former marriage had been any kind of 'child' to Woody Allen; and that there was nothing 'incestuous' about that relationship. If only Mia could get a healthy measure of acceptance of the situation, and to put her children's interest above her own.