fix: Make answers to exercises in 家庭，孩子们 reasonable, as well as correct

[toshify]

• [x] I did all of the following:
  • search for a solution in the discussions
  • search for duplicate or closed issues
  • read the bug report contributing guidelines

Describe the bug

Some exercises have two answer options that are identical, e.g. two 侄女. For 哥哥的孩子, 侄女 and 侄子 are options, but both are semantically correct. This is confusing. The phrase should be 哥哥的女儿 or 哥哥的儿子 respectively.