The sisters later married and moved to other areas. No one any longer remembers the names of the men they married. With the aid of a bride index you might be able to locate a marriage license which would provide the name of the groom. This in turn could help you in tracing the groom's naturalization papers which after 1906 usually listed the name of the wife and in some cases, the date and the name of the ship that she arrived on. This would tell you where to find the passenger list for your grandfather.
Nothing is guaranteed, but it is at least a lead.
I have added over 950 new listings to the 17th Century Residents Data Base and have increased the download speed. Take a look for your elusive ancestors. This is a FREE Data Base open to everyone. The Data Base is limited to postings on Colonial residents, of any name, who were here in this country during the 1600's. You will also find listings of family lines that have been accepted by various societies and organizations throughout the years.