"My parents are affectionate, yet they do not like visitors."
This is an example of "verb second idea" rule. Normally in a sentence you start with a subject (he, she, I, you, the house, cat, etc...) and then the verb comes as the second part (/idea) of the sentence.
In German they like to always keep the verb as the second idea. In english we say "Normally I run". This is German is "Normalerweise laufe ich" - "Normally run I".
As you can see above the extra information at the start means that the verb would not be the second idea unless the subject and the verb trade places.
This is something that begins to come naturally after a while.
If I am wrong at all could someone kindly correct me. :)