I found a similar.question here on stackexchange, but I can't properly understand the answers given there. And the textbook Genki doesn't give much of a detailed explanation on the plural form.
What I've got so far is たち - the ultimate suffix which helps to make the word plural, for example 私たち or あなたたち.
I think it only works with pronouns? If so, can it be loosely translated as "and company"?
But then how can I form the plural form of other words? As far as I know it's not right to add this suffix to every existing noun to make it plural.
For example, if I want to say "pictures", would that be something like 絵画たち or 絵画ら? Or are you supposed to find a proper kanji that represents the plural form in this case?
The other way I know of doing this is to just "double" the noun like this: - やまやま. ２ｘ山 = mountains, right? But does it work for the example above?
And what about ら, eg. かれら. Can it be used for living things etc. as well?
Finally, can you use this way of turning words into a plural form in a formal/informal context?