"Sorry to bother you, I just wanted to know if you are related to a lady who..."
The sentence is incomplete and needs more context to understand the full meaning. We need to know who the lady is and what the speaker wants to know about her.
For example, the full sentence could be:
* "Désolé de déranger, je voulais juste savoir si vous étiez parents avec une dame qui s'appelle Marie."
(Sorry to bother you, I just wanted to know if you are related to a lady named Marie.)
* "Désolé de déranger, je voulais juste savoir si vous étiez parents avec une dame qui habite au numéro 12."
(Sorry to bother you, I just wanted to know if you are related to a lady who lives at number 12.)
The sentence starts with an apology for interrupting, then explains the reason for the question.