"They have no one to respect."
Translation:Nemají koho respektovat.
I get that but I don't get why given that Czech uses double negatives in contexts like this (I thought): "Nemají nic." Not, "Mají nic," And not, "Nemají něco." So to rephrase the question: why isn't the double negatives construct required in the above case, which seems to me almost identical to these other examples?
One possible reason is that "Nemají nikoho respektovat" is also a valid sentence with a different meaning - "They should not respect anyone".
I believe it is mostly just Czech sentences that contain a ni- word that require a double negative. For example, "Nikoho nemá rad." (He likes nobody.)
The word "žádný" also requires a double negative. For example, "Nema žadné jídlo." (She has no food.)
But otherwise single negatives are OK, I believe. For example, "Nemá se o koho starat." (She has no one to look after.)