6)i'd like to know if you'll come to the party. 7) after they'll buy the food,they'll begin cooking. 8) write tp me if you come to moskow next summer. 9) stay here until i return from the bank. 10) before summer will come ,we won't leave the city for the sea. 11) don't go out if it rains. 12) when autumn will begin,the leaves will start falling from the trees.
7) After they buy food, they'll begin cooking.
8) правильно
9) правильно
10) Before summer comes, we won't leave the city for the sea.
11) правильно
12) When autumn begins, the leaves will start falling from the trees.