royal house vs royal line

royal house and royal line both are nouns.

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

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

Other synonyms of royal house include royal family, royalty.

royal house (noun)	royal line (noun)
royal persons collectively	royal persons collectively