] This leads me to the question what could be said about people without risk of being sued? I mean wasn't there even laws agains defaming the Royals?

It apparently depended on who you were. The political artists of the period were seemingly able to get away with anything, but there was clearly a double-standard at work as far as critising the monarchy went. I've got a copy of the Lady's Pocket Magazine or Elegant and Entertaining Companion for the Fair Sex - 1796. It contains the following report for May 2:

On Saturday morning, Kydd Wake, who was tried and convicted last term for hissing his Majesty on the 29th October last, on his return from the Parliament, and crying - "No war! Down with George! etc" was taken into the Court of King's Bench by Mr Kirby, keeper of Newgate, when the following sentence was passed on him, viz. To be imprisoned for the term of five years in the Penitentiary House at Gloucester; to be kept to hard labour during that time; to stand once in the pillory, in the city of Gloucester, within the first three months; and to enter into a recognizance for his good behaviour for ten years from and after the expiration of his imprisonment."

Whew! It's a good thing no-one in authority had read Jane Austen's letter re the Prince Regent.