This expression is taken out of context. Parents share blame when children leave the religion when they do not make every effort to educate their children on the correct path.
An experience was told about a father of many children and he recognizes that the 1st five were given everything towards their spiritual development; but the last two children, parents tired, were not educated spiritually with the same dedication and thus these last two are not as involved in the religion as strong as the others are. So, the parent feels responsible for these last two not being as dedicated in their service to God.
Also, in the same experience was said that a sister married one of the two young men, who at 22 years of age didn't have any privileges in the cong, not even a MS as should be by then; because his non-dedication to the religion, the sister was said didn't have a suitable marriage partner.
This comment didn't imply that sisters only should marry young men who are MS; it's not a guidance or a law, just a comment taken out of the experience context.
GC