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If you state the nature of their work (type of known objects), this will make it easier for someone to research this for you. You have to eliminate the impossible ones to get to an answer.
Mark style with central initials similar to two known artists working with Rancho Alegre found in Mex. menu. Not a conclusion, but a line of inquiry that may yield answers. One other mark belongs to a couple interchanging central letters. Probable dead end there.