Amazing, the same word in Danish and English!
when is it used mine and min?
'Mine' is plural for both common and neuter gender, 'min' is for common gender (en-words) in singular and 'dit' is for neuter gender (et-words) in singular
The possessives follow the grammar rules of the noun.
An 'en' noun has din, and an 'et' noun would get det. In this case it is a plural 'they', thus the 'min' gets a pluralising 'e'.
Det er mine and de er mine both make sense as sentences, and are virtually indistinguishable verbally
My precious XD