Removing a print from a surface is inherently dangerous for the print. A lot of people have lost their family members forever by being hasty.
Before you do anything, make sure you've got a good copy negative or scan of the image just in case you damage the print while trying to remove the lamination. This may be sufficient for your needs and you can leave the print as is and make a copy for yourself.
If you absolutely need the original print, I recommend contacting a print and frame shop that does a lot of archival work. They will have experience removing prints that are stuck to a wide variety of materials. Generally speaking this isn't terribly expensive to have them do the work and they are much less likely to damage the print than you are doing it at home. There is still some risk to the print even with a professional archivist, so don't skip the backup.