Ask an Immigration Solicitor. Get an Answer ASAP.
Good morning, I am Lawyer Ak and I will be assisting you today.
If you and the Mother cannot agree for your son to come and live in the U.K. with you then you will need permission from the Courts before you can proceed with a dependent child visa for your son.
Which visa does the Mother hold for U.K.?
Then her visa will not be revoked for U.K. as she does not have one.