I can't believe some of the responses on here.
Your children have made a choice to call a man they love, and who loves and supports them, Dad.
THEIR choice.
THEIR business.
Why would your sister want to correct and upset your children?
I think she sounds deeply unpleasant.
You have explained that she is upsetting your children and she has disregarded this?
I would stop the calls and I would step back.
This is NOT her business.
I think this is a teaching moment about boundaries and respect for your children.
She doesn't feel she should respect your childrens choice?
Your don't have to have her in your childrens lives.
She is making a big point of sticking her beliefs in the face of your children.
She is not a nice aunt or person.
Step away from her PA behaviour towards your family.
In your place I would be telling her that her views on your family, husband and what your children call him are of no interest to you whatsoever and you don't wish to hear her opinion.
What you do expect is her to respect your children's choice.
If she can't do that, she needs to stay away from your family.
It really is that simple.
A friend of mine some years ago told me how her 6 year old was very fond of her widowed neighbour.
Both her parents were dead.
One day she started calling her Granny and when asked about it, she said if I had a Granny I'd want her to be just like X.
I thought it was adorable and teared up.
Her neighbour loved it.
She is still Granny 10 years later.
Be very firm with your sister.
I bet this behaviour isn't in isolation.
