According to Porcelainmarksandmore the mark on the Royal Princess china is likely a decorators mark,,not a factory mark !! Even though the china was made in Germany many factories sold much as undecorated white ware !! No telling where this was done,, could have been decorated anywhere !!
The best way to sell as a set would be your local Craigslist or any local site !! Just be careful and do not let anyone in your house and always have someone with you when they pick it up !! Weird people in this world you know !! And don`t fall for the scammers !! There are a lot of them prowling the sites !! If you are not familiar with all they do just ask here !! I am usually here daily !!
China has been in a down market lately so check around for pricing !! Not asking prices just selling prices !!