Does the lawful money not remaining in hand after moving to a new house mean that it is unlawful, and how can blessings be brought into it?

You are more aware of your methods of earning money. A mere decrease in blessing does not mean that the money is unlawful. There might be another reason, such as the dwelling. Abu Dawud reported that the Prophet, peace and blessings be upon him, said concerning a dwelling in which the inhabitants and wealth decreased: "Leave it, it is blameworthy." Allah may make the dwelling a cause of harm. If you persevere, pray to Allah, and spend in good, Allah will not disappoint you.