Complex sentence: Every year, the students of 8th grade who are in the Spanish class are visited by the students of Granada in the spring and in the Autumn, when those same students are in 9th grade, they visit Granada in Spain and stay with families.
Split into simpler sentences: Every year, 8th grade students who are in the Spanish class are visited by the students of Granada in the spring. In the autumn, when those same students are in 9th grade, they visit Granada and stay with families.