znát vs vidět?
You probably mean znát vs vědět
znát = 'to know, to be acquainted or familiar with sth/sb'
vědět = 'to know (a fact, an information etc)'
It's kinda similar to 'conoscere' vs 'sapere' difference in Romance languages.
znát = "I know your behavior." Znám tvé chování.
vidět = "I see you in the mirror". Vidím tě v zrcadle.
Why not jejiho? Isnt it meant to be accusative?
Jejího is neuter singular genitive or masculine singular accusative. Here we have feminine plural accusative.
Její could be her/his/it's?
No, only her, it is always feminine.
Elsewhere, when used about a non-living thing, it could theoretically by its, if the thing is feminine in Czech. Růže, její květy jsou červené. Rose, its flowers are red.
What is the difference in Czech between "I know her children" and "I know their children" ?