"Painters and sculptors are authors too."
Translation:Pictorii și sculptorii sunt și ei autori.
"ei" is a pronoun. It means "they". Here it is used for emphasis but not only and refers to the painters and sculptors. Saying "Pictorii si sculptorii sunt autori" means that they are authors. Saying that "sunt si ei autori" it means that they are authors but not the only ones (implies that there are other classes of authors - maybe discussed before). Emphasis falls on "si ei" ("them too" would be a close translation of the phrase) and might suggest that painters and sculptors are not representative classes of authors, so the information is supposed to be "shocking". I'll give you another example: "Pisicile (cats) sunt mamifere (mammals). Delfinii (dolphins) sunt si ei mamifere (not obvious information/emphasis). Hope this helped :)
Articullating (pictorii) is a way to say painters in general, all the painters not only thoose painters. It is different than in English or in German. In those languages, without article means "in general" . In French or in Roumanian you articulate the plural form to indicate The painters (all of them): pictorii , Les peintres ...