Hi Alexsmum, I do think it's unfair of your Mum and MIL to be putting so much pressure on you. That pressure is probably being transferred down to your son who can tell that you are anxious for him to get out of nappies.
I hope I can be of some encouragement - my son is a similar age to yours (2y 10m) and I have only been potty training him for 3 weeks, I just didn't feel he was ready. He would never say if he had done a wee or a poo (well, he would always say 'no poo, no poo' when it was very clearly obvious that he had done one! I had been SO nervous about starting training, I was getting stressed out about it, but I want him to go to pre-school when he is 3 and they have to be dry, so I had to go for it.
My ds is also not a great talker, he doesn't really speak in sentences yet, although I can usually understand most of what he says. But I know he understands what I say to him and can carry out instructions easy, so I thought maybe it was time to try.
I decided to just leave him bare-bummed around the house, with a potty upstairs and downstairs, and told him when he wanted to do a wee he had to sit on the potty. Well, I was amazed! after 2 days and just a couple of accidents he was taking himself off to the potty no problem. I carried on leaving him bare-bummed for nearly 2 weeks so he got the hang of it, then put pants on him around the house. He is a big Thomas the Tank fan, so we found some Thomas pants and I said that if he wanted to wee he had to pull his pants down, as we didn't want to get Thomas all wet, did we? We only had a few accidents with pants on (he couldn't pull them down at first), but he's doing pretty well. He is sometimes wearing pull-ups to go out - he isn't really telling me when he wants a wee yet, but we have been out a couple of times to the local shops and back with pants on. I limit the amount he has to drink, say, an hour before we are to leave and ask him to sit on the potty just before we go out.
I hope that is of some use - good luck Alexsmum, but if he still isn't ready, then don't worry! He will get there and it would really help you if your Mum and MIL could be more understanding and supportive towards you!