How to convince for age to the bride family?

my brother age is 32.The bride age is 24.Bride's mother is telling age is 8year less than my brother.they are expecting unto 29 ONLY.how to convince them to marry? how to make them convince and accept us.

what is the best way to convince them?

NOTE: we like much the bride and the horoscope also good for both.

She is an adult, she can decide for herself.

tell the bride to convince her family, i understand your situation and obviously they only want the best for their daughter, so get her to speak up, its for the rest of her life.

what?