Two mothers and two daughters went shopping. Each bought a DVD with a favorite film and they brought home 3 DVDs. How can thet be?

Напишу на русском: 2 матери и 2 дочери(дочь,мать,бабушка)(допустим: Х,У,С...У и дочь и мать,С и дочь и мать)These peoples are daughter, mum and grandmother