If they were Catholic, I would start with the Mt. Elliot cemetery website. It is actually several of the largest Catholic cemeteries and you can search for free on their site. If you contact them, they will usually get back to you within a week with any info they find. It has been extrememly helpful to me, and sometimes you get additional info, like who they are buried with, and who purchased the plot (which may lead you to other branches you didn't know about). Best of all, it's free!
Good Luck!