So if they balanced out on the machine 2-3 times, they're balanced. To keep balancing them on the same machine and expecting a different result is one of the definitions of insanity.
Same thing with the alignment. If you've checked the alignment a couple of times, and it's spot on, move on to something else. Something's loose, broken, or worn out.
Gradually increase the car's speed in one gear, and pay attention to the speed and rpm that the vibration starts and stops. Check it in at least 2 gears. Do that 2-3 times to check for consistency.
Then get the car up above the speed that it vibrates, like 80-85mph. Put it in neutral, and let it slowly coast down to about 35mph. Write down the speeds that the vibration starts and stops. Do that 2-3 times to check for consistency.
If it vibrates most under power, it's driveline. If it vibrates most coasting, it's suspension.