This is an element of the story that hasn't been delved into yet. Issues #76 and 77 of the regular comic show that Amadeus (and presumably Rosemary) were friends of Jules and Bernadette Hedgehog and other Freedom Fighter relatives. Issue 129 and Sonic Super Special #9 reveal that the two of them were transported off Mobius by the Bem scientist Ceneca 9009 and that Amadeus was Roboticized shortly before Tails' birth. Other than that, we know virtually nothing about Rosemary and Amadeus' history.