Could this be Autism in my 3yr old son?

My step son is 3years old as of this past December. We see him every other weekend from Saturday at noon until Sunday at six. My MIL is an occupational therapist and is convinced he has Autism based on his actions and reactions developmently and socially. He will parrot words, usually no more than two together and even then it's not often he will do it. He won't respond to his name, he doesn't talk or even babble much. He insists on lining up his toys and will lay or sit eye level w/ them and stare then rearrange them, put them back how he initially had them, and stare again. He is painfully attached to this one toy and it must go everywhere. If we pick him up from his mothers and we don't have it he has a melt down. His tantrums are often very extreme, to the point that he will pull his hair and bite himself. Nothing seems to calm him down from them. He has had his hearing checked and looked for fluid behind his ears but everything is normal. His "mother" refuses to have him evaluated because of the sole fact that we want it done because we are concerned. If anyone has any suggestions, or other symptoms I should look for, or any tips on things I could do with him in the short time we get him to help please let me know! (IDK if it's relevant but he lives in an abusive and neglectful enviorment that we have been fighting for 2 years to get him out of. We live in TX and it's a very loyal mother state :( I've heard that enviorment can attribute to autism and other delays) I just want to help my son in the best possible way and I want to get him treatment before it's too late to do so. Thank you for answers, suggestions, tips, and support. It is much appreciated.