1 主谓语都是复数,宾语应该对应为复数 boy friends, cars, houses and social status.
They are choosing not so much boy friends as cars, houses and social status.
2 not so much ...as... 与其...不如说...,第一个句子中修饰的是choose的宾语名词,而在第二个句子中修饰的是choosing,所以as后面也应该用对应的现在分词结构
They are not so much choosing boy friends as choosing cars, houses and social status.