Tracing my grandfather John Malone, born cork 1881, emigrated to Philadelphia

I have been searching and searching for the birthplace of my grandfather. 

We know he was three months old when his parents and older brother left Cork port to Philadelphia. He was born Dec 14, 1881. 

His parents names were John and Ellen and his older brother was John also.  I have been using ancestry.com but to no avail. 

We find lots when they got to Philadelphia but nothing before. 

My Mother would like to get her Irish citizenship and so would I (along with all of our cousins) but we can not do it without his records. 

Do you have a professional we can hire to help?  We would like to buy a family home for vacations for the family but we don't know where they came from.  Can you help?

Mary Packer