royalty vs royal line

royalty and royal line both are nouns.

Word	Noun	Adjective	Verb	Adverb
royalty	Yes	No	No	No
royal line	Yes	No	No	No

As nouns, royalty and royal line are synonyms defined as:

Other synonyms of royalty include royal family, royal house.

royalty (noun)	royal line (noun)
royal persons collectively	royal persons collectively
payment to the holder of a patent or copyright or resource for the right to use their property