First apply water with some dishwashing detergent, many older glue/adhesives will break down in this manner, the detergent keeps the water soaking longer. The only other effective way ( you must be very careful ) is to take a plumbers handheld propane torch and warm each tile, scraping it up with a rigid putty knife one at a time. Be careful.
It can be done, but it will be a nightmare. The damage done to your hardwood floor is likely irreparable, as the glue from the vinyl has likely seeped into the grain of the hardwood. Your best option is to remove the vinyl and hardwood and begin anew.