A court in L'Aquila on Thursday ruled that an appeal by an Australian-British couple against a juvenile court's decision to eject the mother from the foster home where their three children have been living since November was inadmissible.     The couple, Australian Catherine Birmingham and her British husband Nathan Trevallion, had been raising the children, an eight-year-old girl and two six-year-old twin boys, in a house without electricity or running water in woods near the town of Palmoli