You have several pieces of information to work with, and you have given these to this forum. You need to identify the source of the information, beyond just the fact that you have received the information from other people researching this man.
"All I have to go off is his birth certificate which my family already has "
How did your family researcher come by this birth certificate?
Was it an artifact handed down through the family.
Was it acquired since 1915 by a researcher ie how did the researcher know what record to look for?
If you are giving information that you have acquired from other people with an interest in the BROOKS/ROBINSON family you need to identify this to this forum (the fact, not the researcher)
To make best use of the information you are giving us to work with, you need to identify the source of your information.
"all I know" is not very helpful.
Do you have a marriage certificate for the man, born 1915, you are researching?