Here's my analysis of the judgment for what it's worth:
It's an unreported decision of the Upper Tribunal so it is not "landmark" in any way.
The Upper Tribunal's job is to review the decisions of the First-tier Tribunal, but it can only overturn the FTT's decision if the FTT judge made an error of law. It is NOT a forum where the whole thing gets reargued (unless they decide the FTT did make an error of law in which case they will remit it to the FTT to be heard by a different judge or retain it for rehearing in the Upper Tribunal).
It reads to me as though it was an unusually generous First-tier determination. The FTT made findings that the British citizen and her children DID have "family life" with the extended family (not all of them - a few others were dismissed). It is relatively unusual for a tribunal to be persuaded that family life exists other than between spouses and minor children. It has to entail "more than usual emotional ties" that would normally exist for example between adult siblings or adult children.
Having made that finding, the FTT then had to go on to decide whether the decision to refuse was proportionate. It looked at the impact on the British citizens, which seems to have been considerable, and did properly weigh in the balance the impact on public funds and so on.
The SSHD appealed on four grounds. The Upper Tribunal found that the FTT hadn't erred in law on any of those four grounds.
Basically - when an appeal is allowed / dismissed on Article 8, if the judge has written a solid decision showing that they took into account all of the relevant caselaw, weighed in the balance all of the relevant factors, then there won't be an error in law.
IME it is far more common for there to be a harsh decision on Article 8 which the UT will also not interfere with if it is properly reasoned. This one sounds as though it was truly exceptional on the facts, but the judge has properly reasoned the findings and so the UT won't overturn it. The UT can't just overturn because it's not the decision they themselves might have made.