K.A.
As far as your son, everyone has their own timetable for learning to speak and he is responding and communicating, so that is a good thing. My husband was raised in a bi-lingual household so he did not speak fully until he was three. There are lots of reasons why I child would speak late, but some of them are ones where you want a professional opinion. I have seen in other posts where people recommend ECI (Early Childhood Intervention). This is their website: http://www.dars.state.tx.us/ecis/index.shtml. The evaluation is free, but I think he had to be three.
My friend's younger brother did not speak well or clearly. It turned out his ear drums had ruptured from multiple ear infections, and he was not hearing clearly. They fixed that, and he got speech therapy and is now great. Point being it never hurts to have things looked into, and you will either alleviate your worry or get an early start on addressing any issues there may be.
As for your mother, you only have to last until October. Do a lot of nodding and counting backwards from 10. As long as she is right there all of the time, and if you have already told her how you want things done, she is obviously going to keep giving you opinions. If she is punishing him in a manner you don't like, simply walk over, pick up your son, say, "Thanks, mom. I've got this.", and take him into your bedroom until he calms down or you complete the discipline how you see fit. Good luck and lots of patience!!