Second marriage is seen from 9th House. For second marriage the ninth house is considered exactly like 7th is considered for marriage in first marriage Third marriage is seen ---11th house. ..... Some say that second marriage is seen from the third house but I beg to differ. You can check celebrities who have married ( not live in relationship or girlfriend) again and again. And their 9th 11th houses shows the characteristics of their partners.
What if two people have a 1:7 relation in all the Bhav as well as planets in it (except Sun and Moon & different Darkaraka), even different Nakshatra of 7th lord in D9.