So which one of the ten / tamten / tamhleten or tento / tenhle does tehle come from?
HLE is an archaic word for LOOK! If we strech it, tenhle means .this look!.
Té (genitive feminine singular), i.e. genitive of "ta"
When is it člověk and when osoba?
Try to search the forum first, it has been discussed before.
Here you can use both. člověk is closer to a (hu)man, osoba is closer to a person, but there are large overlaps.
But osoby seems plural, so I had written 'these persons', but the correct answer was 'this person'. Why?
téhle osoby is genitive singular
"You are frightened of this person?" was marked wrong. I reported it because it seems the same. In English at least. Not sure how thinly that hair is split in Czech though.