tercer conquanto

My apologies in advance.  I'm sure this has been discussed/explained before, but this is the first time I've run across it.  I'm trying to figure out exactly what would the relationship be in "tercer conguanto de consanguinidad de que eran lejodos".  There is no informacion matrimonial records available (or at least online) to offer more information on the couple, only the matrimonio.  Any help would be greatly appreciated.   Thanks so much.    Alice