Does a tribunal take into consideration where a parent lives? Or are decisions based on where the child lives?

I have been speaking to a parent who has 50/50 custody with her ex-husband. He lives in Camden and she lives in Hertfordshire. Her son has an EHCP with Camden who are objecting to their choice of school in Section I (in fact, in August Camden pushed the whole EHCP onto Hertfordshire Council despite knowing the Mother is about to move out of Hertfordshire).

Because the Mother has to move house (her lease comes to an end in 3 weeks) the children will live with the ex-husband full time for the next few weeks. On 12 Sept, they go to Tribunal to appeal section B, F and I. Will the Tribunal take into account the child is living in Camden at that point? Or does the Mother need to find a place in Camden before the Tribunal date? The outcome they want is for Camden to stop pushing the EHCP onto Hertfordshire and deal with it in borough.