Must I pay the money my mother willed to be paid to our neighbors whom I could not find, especially after my cousin's son saw my mother in a dream asking for money?

You must search for the creditors and pay off your mother's debt, for paying the debt of the deceased is among the most important matters, as the soul of a believer remains attached to their debt until it is paid off on their behalf. If you cannot find them but hope to reach them, then hold onto the money until you can deliver it to them. If you despair of reaching them, then donate the money on their behalf, for Allah does not burden a soul beyond its capacity. As for dreams, there is no place to discuss them.