"other people's plants"? When did plants became personal property within a family? I understand you have your own clothes and other personal things, but plants or pets? People should stop claiming artificial, fine-grained ownerships on everything, within a family. Let family own things. Let family claim the work and achievements.
I have a couple of questions.
When did this person's hobby become your property to cast your whims upon?
If you succeed at proving that they're incompetent, incapable, just holding it wrong, or whatever: Then what? How would this finding improve anyone's situation -- at all, anywhere?