My oldest son and I applied for and received French nationality, our other two children have British Nationality and carte de sejour. I believe my ex-husband (the childrens' father) has taken French nationality by marriage to his second wife.
Would having both parents having French Nationality give the children the right to French nationality too? If so, how could I verify he has indeed taken French nationality.
He lives in France but cut off contact with the children several years ago.
Would having both parents having French Nationality give the children the right to French nationality too?
Not as such, probably because all the other rules (nationality by descent, effet collectif, right to become French for people born in France or for siblings of French citizen who grew up in the country) would make a situation like yours relatively rare. Since your children do not live with their father, his acquiring French citizenship after they were born is generally irrelevant. And to the extent that having French parents matter (e.g. citizenship by descent at birth, double ius soli) then having one French parent is enough, the citizenship of the other parent doesn't matter at all.
That said, there may be other routes for your children to become French depending on their age and how long they lived in France, either as a delayed effet collectif of your own déclaration, because they grew up in France and have a brother who is a French citizen, or if they were born and grew up in France.
If all else fails, it might be advisable to apply for a carte de résident as children of a French citizen (you). This would secure their right to live in France until they qualify for naturalisation on their own. Ideally you want to do that just before they turn 18, in any case before they turn 21, as it might be troublesome to maintain their current status or transition to another one as they become independent. Adult children of French citizens do not enjoy any special path to residence or citizenship in France.
