1)If 7th house lord and Venus in duel sign or duel Navansh sign then dual marriage is possible.
2) Mercury or Saturn in 7th house and 2 planet in 11th house then Native may has 2 wife.
3)7th house lord with natural beneficial planet in own debilitating sign or enemy sign and same time either any of the following combination is full fill
a)7th house has 3 or more than 3 natural malific planet
b)Venus is debilitating with natural malefic or enemy planet
c)8ty house lord in 1st or 7th house
d)lagan lord in 6th house
e) 2nd house lord in 6th house.
4)If 1st house lord or 7th house lord is debilitating or enemy sign or in weak in navmasa then 2nd marriage after 1st wife death.
5)7th house lord is debilitating and associated with natural malefic and 7th house has Gemini, Virgo, Aquarish and Capricorn sign then duel marriage is possible.
6) Lagnesh in 8th house, Mars and Venus in 7th house with Saturn then duel marriage may be possible.
7)Venus in duel sign and lord Venus depositor sign is excellent and 7th house is strong in strength then duel marriage is possible.
8)If 7th from Moon is Venus and Mercury and 8th house lord in 5th house then duel marriage may be possible.
9)If 7th, 2nd and 11th house lord is associated with each other then it may also cause multiple marriage.