"Your sisters are going to my father's restaurant."
Translation:Deine Schwestern gehen ins Restaurant meines Vaters.
Genitiv isnt so bad. Just rember "des der des der" for "der die das die" for the articles.
Nouns in genitiv usually get an -s or -es suffix (though some are irregular).
The modified article + word order will then indicate possesion like "of a (eines/r)", " of the (des/r)", "of his (seines/r)", etc.
So "Restaurants meines Vaters" == restaurant of my father('s) == my father's restaurant.
In a lot of cases you can just put the 3rd noun ahead of the 1st and tack on an 's to make sense of it in English.
And this link is good for all the cases: http://www.nthuleen.com/teach/grammar/nomakkdatexpl.html