Only a fool who has zero knowledge of Sanatan Dharma would ask such an obscene question. Before making such an idiotic question, understand who is Brahma Dev and Maa Saraswati.
Brahma Dev is the creator of the universe. When a desire for a female companion rose in His heart, He split himself into two halves. His another halve came to be known as Devi Saraswati, and she is his Wife, not his daughter. A Daughter is born when a male and female consummate.
Maa Saraswati is the Goddess of Knowledge. To create something, one needs to possess the knowledge of the process. With the help of Maa Saraswati, Pita Brahma Dev created the universe and all the beings. Through his consciousness, He created 7 Manas Putras, the 7 sages.
The same is the case with other Gods of our Trimurtis. Prabhu Shree Hari Narayan's other half is Maa Laxmi, while Maa Parvati is for Prabhu Mahadev. For Indra Dev, it's Indrayani or Shachi Devi. This is what Ardhanareshwar or Ardhanareshwari is all about.
There is no difference between Prabhu Brahma and Maa Saraswati. They both are the same just like Shree Hari and Maa Laxmi, and Mahadev and Maa Parvati. That is the reason we call our spouse or wife our better half.
A Daughter is born when a male and female consummate, not our other halves! Some think as Prabhu Brahma looks old, He's Her Father. But that's not true. Prabhu Brahma’s hair is white not because He is old, it actually depicts his immense experience in creation & wisdom.
All the above information is written in our Upanishads. So all those who love insulting Sanatan Culture and our Tridevs and Trideviyas… Raise the bar of your IQ level, read the books and only then open your mouth.