Ive used some like that - they can be dicey.
First overspray with some sort of clear, gloss coating. I use regular acrylic enamel (Im oldschool; we didn't have a dedicated product for everything back in the day ) You will have to cut them individually from the sheet as already mentioned, but the coating holds them together.
Then dont soak the decals - never soak decals. Dip them, place them on a wet sponge or paper towel and let them absorb. Then place them using either Future/Pledge or the white glue trick mentioned by 511inf.... well that guy up there. These two compunds, PA glue and acrylic finishes are your friends when dealing with old decals.
In the end, its probably going to be simpler to get some AM decals. But what model builder is about simple?