All they will need to do in 30 or 40 years time is say that "we understand that Jesus evidently meant 3 sucsessive overlapping generations" and whoever is still a JW then will lap up the urine they serve.
It could be presented like this
Hahahaha... "evidently Jesus is referring to generation based on the family unit : What is a family unit commonly made up of today ?
Grandparents, parents and children ... this generation can span 100 years or more . Also today it is not
uncommon for families to even reach 5 generations !!!