The ancient Christian teaching on the two-fold purpose of marriage; namely, the “procreation and education of children,” and the “mutual help and sanctification of the spouses,” accurately summarizes the inner order of marriage. As the future John Paul II wrote in his great 1960 book Love and Responsibility, radical personal openness to both of these purposes is essential to the success and meaning of any marriage. We should never enter into marriage with active opposition to the very ends for which it exists. If a couple is preparing to embark upon marriage with the immediate intention of avoiding offspring (even if they are using morally acceptable means such as NFP), they perhaps ought to consider delaying the exchange of their vows until they have resolved the various impediments, whether financial, career-related, or personal, that are leading them to be closed to the idea of having children. Yet the very same denomination, the RCC, says Joseph and Mary did not have any children of their own.
Based on the above position of Roman Catholicism, they never should have entered into marriage.
Fortunately, we know the NT tells another story that Joseph and Mary did have kids of their own.