@Louise ********
, he can travel alone to get his new stamp. You and your daughter are fine until 8th Oct. No need to travel with him for his new stamp. As you described, get him to enter again within visa is valid, then you and your daughter can go to the local immigration office to apply for an extension matching his stamp on or before 8 Oct.
(I just saw 8 Oct is Sunday, you need to apply for your extension within 6 Oct)