S.H.
Okay, he has Anxiety.
But... the KEY thing is now what?
He NEEDS to learn, (and the Therapist should be doing this), is he needs to learn "Coping-Skills."
And how not to use it as a default, excuse.
I would get another Therapist.
2) Next: IF he had a true condition, such as "Anxiety".. then this would be present, anywhere anytime. BUT, you said your son ONLY does this with you and your Husband. NOT at school and NOT with his Nina.
SO... there is a discrepancy. Because, if a person has a condition, it would be present... and not just at certain other places.
What is his relationship, with you/Hubby?
Again, a child needs to learn Coping-Skills.
Because, their environment and social situations cannot be controlled. Thus, they need to learn how to COPE, as a whole.
And just being a part of society, they will encounter a myriad amount of situations.
OR, is it simply something like, he feels usurped by his sibling???? Is this sibling younger or older or a new baby in the house?
So you have to consider that too.
Also, if he is always 'expected' to behave correctly and more grown-up than he is, that can frustrate a child and if they don't have validation or know coping-skills or no one relates to them, they get all sorts of icky behaviors. Maybe they just want/need more attention/bonding with their parents/and to feel, good.
How does his Nina treat him?
Why is it, that he is fine with her?