This is very sad and you must be devastated to be cut out of this little boy's life. Are you not able to see him when your daughter has access? It does sound as though he needs to see someone who would be able to assess him before he gets much older - does your daughter agree he needs some help? If so could she contact the services who have dealt with her access to tell them of her/your concerns? As Doodle has said there are many people on the autism spectrum and go on to live happy and productive lives. If he is then it should be picked up in school.
He sounds very like my own little grandson who is 5 and was diagnosed with high functioning aspergers last year. He's extremely intelligent but has some behavioural issues which make him unable to control his emotions at times. My son had suspected there was something from early on and eventually they paid to have him assessed before he started school last October. He is now going to have a teachers aide as there are some things he can't cope with/doesn't understand. They live in NZ so we have only seen him twice but he was here Christmas 2016 when he was 4 and we also realised he was not a typical 4 year old but he is a lovely little guy and very special to us all.
Try not to worry too much.
I've got another 'keen'... Ouch!