эстонских

In a sentence

• Я был на выставке эстонских картин.

  I was at an exhibition of Estonian paintings.

  In this sentence, 'эстонских' is an adjective in the genitive plural case, describing the origin of the 'картин' (paintings).

• 'Эстонских друзей мало, но они верные,' сказала она.

  There are few Estonian friends, but they are faithful, she said.

  Here, 'эстонских' is an adjective in the genitive plural case, modifying the noun 'друзей' (friends).

• Я читала книгу об эстонских художниках.

  I read a book about Estonian artists.

  In this instance, 'эстонских' is an adjective in the prepositional plural case, as required by the preposition 'об' (about), describing 'художниках' (artists).