**EDIT**
Okay so after running these again to test, the following method works great for hard. For the medium ones I recommend doing 2 drops, then clearing notoriety before you start your third.
If like me, the hard rated Snatch missions are making you pull your hair out, I have some tips that will make it much, much easier (on all difficulties)
Before you start, have a look at the Snatch location icon on the map, and buy some properties near that marker. The route it suggests for pickup really doesn't stray far from that marker, so get 1/2 properties/stores close to it.
Start the mission.
Drive up to the targets and kill them from the car. Or get out, whichever is easier for you.
Leave the girls there for now, do not press
yet.
Drive to your property and merely enter it to lose all notoriety stars.
Drive back to the girls, press
to get them in the car hassle free as you now have no notoriety.
Drive to the blue marker to drop them off.
Rinse and repeat.
You might think this is too time consuming, trust me it isn't. I had plenty of time left on even the hard ones.