Do you live in the U.S.? If so, he would qualify for developmental preschool with a language delay. Developmental preschool is free through the public school system. My daughter is turning 3 next week, and she is starting next week. She had therapy in the Birth to 3 program until now. Now we're transitioning.
My daughter was diagnosed with pervasive developmental disorder (PDD) on the autistic spectrum (she's too young to diagnose between PDD-NOS and typical autism, so it's not specified yet). She is usually very social and interactive, but in her own ways. Her eye contact is really good. She has problems with social cueing and huge problems with speech and language processing. And she has sensory issues, ritualistic behaviors, and other things that are typical of autistic behavior.
Anyways, you could express your concerns with your son, but in the end, they are the parents and they have to make the decisions. I have a dear friend with a son who has significant language delays (no other delays or issues, just language). He could qualify for free developmental preschool but she chooses to keep him at home and not send him to public school. She can't send him to private school yet because he's not toilet trained. And she refused the Birth to 3 speech therapy for him as well. He has made very slow progress compared to my daughter (they are the same age, only 1 week apart). I mentioned the things to her, only because my daughter has and will be going through them, but after that I don't suggest things because I know she gets frustrated because she hears the same things from her family. Well, anyways, just wanted to share my friend's frustrations, to possibly save you some heartache if you have an argument with your son about how to raise your grandson.
Is your grandson learning sign language? It's a great bridge for communication until the spoken words kick in. You don't even have to see a therapist to teach them. There are so many children's sign language and baby sign language books out there since that is the popular thing these days.
If you click on the Health Page icon on the top right hand corner of this page and go into Behavioural Characteristics behind a Diagnosis of ASD, I have posted the clinical criteria. These are the lists of behaviours that professionals are looking for to diagnose a child/adult as being on the autistic spectrum. Parents have also posted examples of their child's behaviour that fits the criteria to help others understand what kind of behaviours the professionals are looking for.
Have a read through that and then post back again with your thoughts.