Thanks for your question.
The British Encyclopaedia 1933 vol7 p90
...the parties must not be within the prohibited relationships, namely, ascendants and descendants ad infinitum, brothers and sisters, and collaterals where one stands in loco parentis to the other (e.g. uncle and niece), half-blood relationships, and the corresponding relationships by affinity (excepting, by recent enactments,-Deceased Wife's Sister's Marriage Act 1907- the case of marriage with a deceased wife's sister or a deceased husband's brother) being prohibited equally with the full-blood.
The British Encyclopaedia 1933 vol6 p99
INCEST, sexual intercourse within the prohibited degrees, which by the laws of England and Scotland are founded on the Levitical code [see The basis is Leviticus 18:1-17], and include degrees both of consanguinity (lineal descent) and of affinity (kinship by marriage). (Cf. Lev. xviii)...
Marriage to a brother’s wife (presumably divorced - as death annulled marriage) is singled out with a special penalty in Leviticus 20:21. This was what John Baptist reproved Herod for in Mark 6:17 and Matthew 14:4.
The exception: The Levirate Law, from Latin levir, "a husband's brother", took precedence if a man died without issue. His brother was required to marry his wife and their firstborn would succeed in the former’s inheritance to preserve his family’s line in Israel. See Deuteronomy 25:5,6
The Law of Moses is not in force amongst Christians but we are subject to the laws of the country we reside in. However, the principles laid out in Leviticus are sound advice. The dangers of ‘inbreeding’ are well documented.
The law of Christ, requiring us to love God and one another, should be sufficient to keep us from dishonouring one another in the sight of God in the way that Leviticus 18 prohibits.
I hope this helps.