in vedic it's about a balance of malefics and benefics not just the 7th housemars in certain houses (off the top of my head 2 and 4 because my fiancee and i both have this) can make someone manglik, but 2 people with those placements wont feel an effect from each other, being born on a tuesday can cancel it out, benefic venus can cancel it out so on etc
ruler of the 7th house in the 6th etc
rahu with venus or moon, rahu in 7th and a shitton of others these are just off the top of my head
things cancel it out, things balance it
keep in mind vedic is also based in indian culture and very traditional so multiple "marriages" could also just be multiple partnerships, could also indicate a separation then getting back with the same person etc and so on
certain things like malefics in the 8th and 12th house if venus is aspected by certain planets in specific positions can indicate remarriage through death of a spouse and then you also have to look at the d9 chart (which is probably why you're thinking of the 9th house) for additional details