The Lu family and the Jiang family had substantial economic disparity. Perhaps in the eyes of others, the Jiang family had climbed up the social ladder. The Lu family might not treat the Jiang family very well.
However, Mr. Lu and Mrs. Lu were clear about their relationship. They both knew that a daughter-in-law was equivalent to having an additional family member. If the daughter-in-law's family were a mess, she would be the same as well.
Mrs. Lu was satisfied with the Jiang family. Even though Mr. and Mrs. Jiang did not have much education or money, they were reasonable people. Most importantly, no one in the Jiang family was greedy. That was the rarest thing.