What is the ruling on furniture with which a house was furnished using money deposited in non-Islamic banks, following previous fatwas that permitted it, then the unlawfulness of this transaction became clear later on?

There is no objection to using the aforementioned furniture, as the prohibition does not relate to it. However, you should advise your mother and mother-in-law to stop depositing money in usurious banks. Interest on loans, opening credit accounts with interest, and all types of lending for interest are all prohibited usurious transactions, as affirmed by the Second Islamic Conference of the Academy of Islamic Research in Cairo.