we aren't told the matter between anamika, her hubby and rhea...i dnt think we have..but mamta and akshay know them because sid once saved mamta and bought her to hospital and they saw him, but sid's memory has gone and he doesnt recognise them where as they do, and slowly slowly circumstances forced mamta n akshay 2 believe that Arjun is sid... and so mamta is trying her best to make sid get his memory back...and i guess anamika found sid after his accident, treated him and let him stay in the house, telling him he was Arjun, Rhea's dad and her hubby...
hope that helps..if im wrong please someone correct me because i have been skim reading updates im reali busy thats why.