A good first effort at taking the sensory details of this simple domestic scene. One technique for this type of writing is to avoid saying 'I heard, I saw' and experiment with describing what is happening :
Instead of "I focused more on the sound of the kitchen I was observing, I could hear the rumble of the 40 years old fridge like it is old, as my two grandparents but who were making less noises. "
Try : The forty year old fridge whirred and rumbled in the kitchen as my quiet grandparents finished dinner. OR The sound of my grandparents in the kitchen was covered by the rumbling old refrigerator.
Instead of "The 4th chair was filled with the hairy cat called Fauvette"
Try : "Fauvette, our hairy family cat, purred lazily / reigned imperiously / spread herself out lazily in the empty chair."