Planck scale units aren’t known or typically assumed to be minimum units. They’re just the units that come out of combining some fundamental constants and are thought to represent a scale where the effects of quantum gravity have too much effect to be ignored. They just represent a theoretical limit to the validity of our current models.
Human knowledge will continue to push these boundaries as long as humans still exist, but it’s arrogant to think our current human limitation is a universal limitation.
Genera are within families, not the other way around. Maybe read a book?
Also: the genus Panthera consists of 5 big cats. The other two big cats that aren’t in Panthera are the cougar, which is also colloquially called a panther, and the cheetah.
So, in fact, “panther” can refer to any big cat other than cheetahs.