Translation:They told me that they like to read the newspaper.
If you embrace your inner Yoda and break it down hyper-literally you get: "(to) me they have told". The sentence tells us who did the telling so we need to include that in the English translation.
(loro) hanno = they have, using the "hanno" form of "avere" implies the "they" so "loro" can be omitted. detto = past participle of "dire" = to tell
I hope that helps :)
Nope, since "piacere" in Italian has the "thing being liked" as the subject, and the "liker" as an indirect object.
In this case, the subject is the sentence "leggere il giornale", so you have 3rd person singular (piace). By the way, 3rd p. plural would be piacciono.
See it as "Reading the newspaper pleases them" = they like to read the newspaper.