Advice Needed: She Doesn’t Want To Change Her Name After Marriage

An NGLatest reader sent this in. Kindly drop your advice:

My big bro is currently in this dilemma..
He has a fiance ..They’re wedding date has been set already(although they have not started printing the Invitation card)..

three weeks he was jokingly playing with his girlfriend(wife to be)
when he uttered the statement “Very soon you’ll be known as Mrs
Adekunle” (not the real name)

Then the girlfriend responded that
she wants to keep her surname and add it to the guys surname… that she
doesnt want to completely throw away her surname
My bro rejected the idea.. it all started like a joke but now its a big problem

My bro is threatening to call off the marriage just because of this funny issue
The girl is also forming “strong head” claiming she will stand by her decision (NB shes a lawyer by profession)
Funny enough her mum is also fully behind her(her dad is late)

My brother said its either she sticks with only his surname or He calls off the wedding

My brother loves the girl.. and I know she loves him too
Do you think my brother is being immature with this issue?
Should my brother go on with the wedding or should he Call it off??