Belle didn't have any experience of meeting someone's relatives in her whole life. When Emilia set her up on a date with Prince in the past, only the two of them would meet in the café. Sometimes, he would even bring his girlfriend to join their date so that the latter would avoid feeling jealous. Prince's mother didn't like his girlfriend and wanted Belle instead. Belle didn't like Prince because all she ever thought of doing was to work and give Neon a better life. She only met him to stop Emilia from getting disappointed. Prince also met her because he couldn't disobey his parents.
During the times that she had been 'dating' Prince, which was roughly 6 months before she went on a medical mission, she met his mother several times and that was when Emilia brought her around. She never met the woman on her own. Prince's father was a busy businessman and was always away for business trips. He rarely goes home, and Belle only met him once during Prince's birthday.