As for why Nangong Shulan is thinking of helping the Qins, there are a few reasons. Firstly, they have helped her and her two children over the years. Secondly, they have never done anything to wrong her. The most important reason, however, is that they are her husband's elder brother and his wife. If the two brothers united, no one would dare to bully the Qins. Now that her family is doing well, she wants to give them a hand. This was also her elder daughter's idea.
Her elder daughter had written recipes for her and suggested they could be used for her eldest uncle's family. Her daughter said they should first get themselves settled before sharing the recipes with the Qins. This way they could check whether her uncle's family would become jealous because her family is making money, or if they'd have some reliable people to help them once they got settled. This would be much better.