Sounds like they need to form a co-op. Each member signs their 2 plants to the co-op to manage/grow/etc. Pay the members something for their "license use". I'm guessing there are plenty of people that would never attempt to grow those 2 plants on their own, so don't let it get wasted.

Also, limit the co-op to be run by citizens of that country/city to keep it from becoming international rings (bwahahahaha, as if that would work)