How to handle dependent FB (learngitbranching)

gistfile1.txt

{
  "goalTreeString": "{\"branches\":{\"master\":{\"target\":\"C10\",\"id\":\"master\",\"remoteTrackingBranchID\":null},\"FB1\":{\"target\":\"C7\",\"id\":\"FB1\",\"remoteTrackingBranchID\":null},\"FB2\":{\"target\":\"C9\",\"id\":\"FB2\",\"remoteTrackingBranchID\":null}},\"commits\":{\"C0\":{\"parents\":[],\"id\":\"C0\",\"rootCommit\":true},\"C1\":{\"parents\":[\"C0\"],\"id\":\"C1\"},\"C2\":{\"parents\":[\"C1\"],\"id\":\"C2\"},\"C3\":{\"parents\":[\"C2\"],\"id\":\"C3\"},\"C4\":{\"parents\":[\"C2\"],\"id\":\"C4\"},\"C5\":{\"parents\":[\"C3\"],\"id\":\"C5\"},\"C6\":{\"parents\":[\"C3\",\"C4\"],\"id\":\"C6\"},\"C7\":{\"parents\":[\"C3\"],\"id\":\"C7\"},\"C8\":{\"parents\":[\"C6\",\"C7\"],\"id\":\"C8\"},\"C9\":{\"parents\":[\"C5\",\"C7\"],\"id\":\"C9\"},\"C10\":{\"parents\":[\"C8\",\"C9\"],\"id\":\"C10\"}},\"tags\":{},\"HEAD\":{\"target\":\"master\",\"id\":\"HEAD\"}}",
  "solutionCommand": "git commit;git checkout -b FB1;git commit;git checkout master;git commit;git checkout FB1;git checkout -b FB2;git commit;git checkout master;git merge FB1;git checkout FB1;git commit;git checkout master;git merge FB1;git checkout FB2;git merge FB1;git checkout master;git merge FB2",
  "startTree": "{\"branches\":{\"master\":{\"target\":\"C1\",\"id\":\"master\",\"remoteTrackingBranchID\":null}},\"commits\":{\"C0\":{\"parents\":[],\"id\":\"C0\",\"rootCommit\":true},\"C1\":{\"parents\":[\"C0\"],\"id\":\"C1\"}},\"tags\":{},\"HEAD\":{\"target\":\"master\",\"id\":\"HEAD\"}}",
  "name": {
    "en_US": "How to update a depending FB when the original FB is updated after fork"
  },
  "hint": {
    "en_US": ""
  }
}