DD, I think your instinct is right. Something is not adding up. It could be something as simple as his ears, it could be more.
Go to a GP and asked to be on care plan(they were called enhanced primary care plan or EPC) where you get so many of each of therapies you are talking about. At the moment, you are stuck in the system and it can have very long waiting lists. In the mean time, a GP that bulk bills could put on a care plan that that refers you to an OT, Speech and also psychologist if need be that bulk bill through the care plan.

You need to sit your DH down and explain he cannot say those things to his DS, I suppose it needs to be put in a way that he gets it as well, treat others how you wanted to be treated kind of way, children inlcuded. Little children are a lot smarter than we give them credit for and I am afraid it's not helping your little man.

Alot of places will offer free hearing tests, again check with your GP.

Early intervention is always best. Good luck.