What can be done if an estate owes money but won't pay?

When your husband's brother passed away, you should have submitted a claim against the estate and then followed up with a lawsuit for back rent.  if there was no contract signed for your brother in law to use the space, then he was considered a month to month tenant.  if he was a month to month tenant then you should have terminated the lease on the day he died and the estate is liable for the month that he was renting the space and failed to pay.  I suggest that you file a complaint aganst the estate now and serve the executor.  the executor will be required to then hire a lawyer.  the estate will likely show you the acounting it did and will say the estate has no money left.  if this is the case you wil probably not collect any money.  if the building is yours, you should find a new tenant.