Hi, sorry to hear you are going through this, it never seems to end does it? Slightly different way round but hope it helps.
My daughter wanted to change her surname from her Fathers to match that of my second husbands (the reasons for it are a different story). After much research we found we could do it via
Deed Poll if her Father agreed. At first he understandably denied her the permission, however after a year of asking (pleading) we had to tell him we were prepared to take it to the family court as this was the only way we could do it and it was becoming a real issue for my daughter.
He was understandably upset but when he realised how serious she was and that the court was likely to listen to her views and grant in her favour (she was 12) he agreed. We changed it via
Deed Poll but we had to have a signed agreement from her father.
It''s my understanding after much research that your ex could only legally change their surname if
a) you give written consent and its done via
Deed Poll
b) by taking it to court in which case it would be because it''s what your children want not their mother & it can be proved it would cause considerable psychological damage they didn''t get a name change
c) they reach age 16 and can decide themselves
I hope this helps, don''t feel bullied into agreeing, my ex tried to bully my daughter into keeping her surname and it caused a lot of distress. She is so much happier now and more comfortable with her identity, never underestimate the importance of a name and its associated identity, agreeing to the change could cause upset for your children their Mum hasn''t yet considered.