Sending emails to Custom Field email ids.

I have created custom fields for email ids, with names like Mother email ID, Father email ID, etc.

I can search leads and contacts by manual search criteria, for example: Father email ID - is not empty. and i get results.

But the problem is: I cannot send mass emails to father email ID or Mother email ID. Can someone guide me how to select and send mass emails to custom field email ids?

P.S: I need to send an mail to Primary + Custom Field email ids.

I also need to send mass emails to ONLY: Custom Field email ids. (i.e. Avoid sending certain mass mails to Primary email IDs.)