Does the Old Testament levirate marriage law still apply today?

That does not apply anymore. We do not take up our brother's wife if he dies; we have a thing called life insurance. In those close-knit communities, which were sometimes no more than a thousand people, you did not have a life-insurance pool you could pay premiums into to provide for a wife after her husband died; the family took it over. But that is not modern times, and it is not required, because we no longer live in the Old Testament under that set of civil laws; we live under a whole new set.