“法律上不允许近亲结婚”用英语怎么翻译？

近亲结婚 在科学术语中叫 consanguineous marriage

这句可以这样翻译：

Consanguineous marriage is prohibited in law.

CLOSE RELATIVES ARE FORBIDDEN TO MARRY ACCORDING TO THE LAW

Marriage of close relatives is forbidden in law.
或者： It is forbidden in law for the close relatives to get married.