The problem is that woman as a social definition means things which are not financially rewarded or equitable in society.
In the nineteenth century, the social and legal meaning of being female was that a woman was her father’s and then her husband’s property, without equal access to education and employment (because she was biologically female).
The social and legal meaning of being female was that a man could rape his wife till 1990; that he could have sex with her when she was asleep and it not be rape until 2010 (Scotland).
Those are the gendered social norms attached to being female. Gendered social norms have changed enormously to the benefit of women in the last one hundred years. All the opportunities which your husband’s daughters have are due to feminism rejecting and challenging gendered social norms.
Ask your husband if he understands and agrees with that assessment, that gendered social norms are cultural and malleable.
If he agrees this, why on earth would it follow that gender is innate?
Gender is the set of socially constructed norms which male and female bodied people have to accept/negotiate/resist/challenge in the world. Gendered norms are not static, so how can gender be innate? It is not because what gender means changes over time and depending on place.
If he believes that his daughter’s are equal citizens in the world, why would he subscribe to an ideology which inscribes certain characteristics to women? Characteristics which happen to lead to less financial reward and more sexualisation?