Send them a letter by certified mail, return receipt requested, informing them that the landlord has passed away and that they should forward all future payments and notifications to you, the executor of the estate, and give them an address. Make sure you give them a phone number for emergencies. Also send a copy of the letter by regular mail and make a notation at the bottom of the letter that it was sent by certified and regular mail. This way if they refuse to accept the certified mail they can't claim that they never received the notice.

