No, the word 'they' is not a noun at all.
The word 'they' is a personal pronoun, a word that takes the place of a plural noun or nouns for two or more people or things as the subject of a sentence or a clause.
Examples:
The Browns came to visit and they brought the baby with them.
Jack and Jill went up the hill. They were fetching some water.
Note: The corresponding pronoun that takes the place of a plural noun or nouns for two or more people or things as the object of a verb or a preposition is 'them'.
No the word notes is a plural noun. The singular noun is note.
The singular form is phenomenon.
Yes the word formation is a singular noun. The plural noun is formations.
The word army is a singular noun; armies is the plural form.
Yes, the word 'friendship' is a noun; a singular, common, abstract noun; a word for an emotional relationship between people; a word for a thing.
The noun personalities is the plural form for the singular noun personality.
The word tooth is the singular noun. The plural noun is teeth.
The word finder is the singular noun. The plural noun is finders.
The word actress is the singular noun. The plural noun is actresses.
Yes the word question is a singular noun. The plural noun is questions.
The noun garb is used as a group noun to mean clothing. It uses singular verbs.
The word aisle is a singular noun. The plural noun is aisles.