Thanks for the feedback.
Daughters must have their husbands surname in order to be married in the initial family tree and belong to their family.
Hmmm did you mean "must have their husbands surname" or "must have their fathers surname".
Because this seems to work ok, and in this case neither Kyrstyan nor Tillote have their husbands surname:
Code:
character Henry Cracker, named character, male, leader, age 58, x 11, y 122
traits Factionleader 1
army
unit NE Bodyguard exp 1 armour 0 weapon_lvl 0
character Charles Lambert, named character, male, age 29, x 7, y 138
army
unit NE Bodyguard exp 1 armour 0 weapon_lvl 0
character_record Kyrstyan Russell, female, age 57, alive, never_a_leader
character_record Tillote, female, age 20, alive, never_a_leader
relative Henry Cracker, Kyrstyan Russell, Tillote, end
relative Charles Lambert, Tillote Cracker, end
I also tried this one which doesn't seem to work:
Code:
character_record Kyrstyan Cracker, female, age 57, alive, never_a_leader
character_record Tillote Lambert, female, age 20, alive, never_a_leader
relative Henry Cracker, Kyrstyan Cracker, Tillote Lambert, end
relative Charles Lambert, Tillote Lambert, end
Seems that for a daughter, they always inherit their fathers surname, and if they are married you can't change it because the system expects the character to have their fathers surname 
I've had a look at vanilla and a few mods and can't find any examples that prove otherwise unfortunately.