kerry, I soooo know what you're going through at the moment. I had the exact same issues with my DH and his family. My MIL persisted in telling people she was coming despite being told otherwise and my DH didn't understand why I was so adamant that she wasn't and that I didn't even want his family to know I was in labour. Funnily the only person in DH's family who understood was SIL who had also banned MIL from the delivery (but not from the hospital so she and SILs MIL pushed thier way into the room before SIL delivered the placenta!!!)
We argued about it heaps but I stood my ground and DH eventually accepted that although I wanted him involved in the delivery it was on my terms. I think that its important that you stick to your guns becasue stress in labour can actually slow it down or even halt it altogether. I also think that having some privacy straight after the birth is really important. Firstly because you need it to bond but also because by the time you've given birth you might feel like half the staff at the hospital has had a look at your privates so a bit of time alone can be a massive relief (it was for me anyway). If all your ILs are waiting you may feel that you have to rush that time or even find it denied to you.
Your ILs will just have to get over it. After all labour and birth is just a beginning and they have many years to get to know your baby.
As for your mother telling people she will be there - my MIL did that too and although it annoyed hell out of me once I was sure that I had repeated and clarified my position I just let it slide. It made her feel better even if it was a total fantasy.