How easy would it be for Step-Mom and Father Getting Custody Of Minor Child in BIO Uncles Care

My boyfriend and i have leagal guardian ship of his 2 year old nephew. the nephew has lived with us since the end of Jan 2012. we went infront of a judge in IL, judge granted us full custody guradian ship on May 31,2012. His parents who are not married or together visit/see him from time to time with no consistancy. Now his step-mom is telling me that her and the father want him back full. They can barley afford each other and her son. They live off the state and anything they can get. The minor child's uncle and I support him with no help from anyone, nor have we asked for any help. We are trying to do whats best for the child, he lives with us, has his own room, hes always clean and fed. We had to have 2 teachers come in every week to help with his learning because he didnt talk when he came to live with us. Now that he has progressed and is able to tell you what he needs. the father and step mom want to take him away from his only steady home he knows.