You need level 2 of Pickpocket for the people in the quarantine area. You can also kill one of the cured people to get a potion back for the third (no reputation drop), though that kind of defeats the purpose.
There are a couple bugs which will let you duplicate the potions, as well.
<span class='standouttext'>Spoiler : </span><span class='spoiler'>To copy an item; quick save the game, then drag an item out of your inventory, but not somewhere there is a red X. Without dropping first, quick load the game, then release the mouse button when it starts to load. This will produce a copy of the item on the ground, with the original still in your inventory.
There is a much easier method for items which can be stacked;
Drag a stack out of (or into) your inventory (or container) and hold down the control key before dropping. This will bring up the split stack pane; type in a negative number and hit enter (the checkmark will be greyed out). This can also be done in the trade window.</span> (highlight the text to read)