Mozart influenced more unified and expressively fuller imitation in orchestration. He also influenced the psychological use of the orchestra in operas for background effect on the audience.
Haydn's early home life influenced his music and gave him humility. He was born into a poor family and grew up hungry. He left home when he was 6 to become an apprentice and fell in love with music.
Mozart's early home life influenced by the love and support his family gave him. He was born into a finically fairly well off family and grew up with six siblings. He left home when he was 7 travelling with his father until he had his first piece published.
Because he was so much older, Haydn influenced Mozart to write string quartets. We learn from their letter to each other that Mozart thought of Haydn as a second father. They played music together on many occasions. Haydn would play the violin, and Mozart would play the viola. They both had a major impact on classical music, which still impacts today.