If a boy touches his sister out of lust, does this terminate their parents marriage?
If a brother touches his sister out of lust and desire, that could be due to the poor and weak upbringing of the paents. If the parents nurture their children and guide them to the path of morality and shame, then such immoral acts would not take place.
Nevertheless, if a brother touches his sister out of lust and desire, that does not terminate the Nikah of the parents.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai