Make sure that you get 'Only DH allowed in delivery room/until 12 hours after birth(or whatever you think is appropriate)' written on your birth plan and notes - not that they will necessarily look at it at the right time but if it is there then it is another line of defence against having anyone else in the room with you and you can wave it at the staff to get them to help you remove people if you need them to.
Just because 2 people are allowed doesn't mean that you have to have 2 people with you - some people might want to take their mum or a friend or a doula with them as well as their dh but they should certainly respect your wishes about visitors if you only want your dh.
as everyone has said, get your dh to turn his phone off and not call anyone until after the baby is born and you are ready to have visitors... and get him to start not returning calls (to parents!) immediately from now on so that they don't start to assume that the baby is being born the moment they can't get in contact with him.
get him on side too - before he starts getting carried away with his thoughts of how nice it would be for him to be supported by his mum at this difficult time for him , get him to imagine that the situations were reversed; he is lying in a hospital bed virtually naked, having spent the previous 1-36 hours (go for the worst case scenario to really hit home, sorry, don't want to scare you but want to scare him IYSWIM), all bloody and in pain and completely exhausted and waiting to deliver placenta and know that you are about to have stitches - plenty of other examples in this thread - not forgetting of course that he would have spent lots of HOURS trying to poo out a watermelon - or pee out a large grapefruit.
Would he want your mum to come in and have a chat with him right there and then or would he expect her to wait for him to clean up and get sorted? Chances are that he is not going to want to be chatting to her immediately regardless of how much he likes her! so hopefully he will see that the same holds for you too, the hospital has visiting hours for good reason, that much as you love your MIL and are excited about her meeting her grandchild, until a baby has been born nobody knows what the birth is going to be like - it could be an hour or two, it could be a day or two or end up needing intervention.
and nobody knows how they will be afterwards, so you don't want to commit to anything beforehand - could you in conversation say to your mil something along the lines of 'from talking to m/w, not sure how long these things take and how long it will be before we (ie you / dh / new baby) are ready to see everyone after the birth and all the sorting out afterwards - if it has been an easy birth and it is daytime then maybe a couple of hours to get everything sorted, but if it is nightime and/or if has been particularly long or problematical then they say it is a good idea to try to have the first breast feed and first mother and baby nap before seeing anyone else, so maybe it will be six or seven hours before we invite visitors - and obviously we all want what is best for the baby on it's first day'.
That way at least your MIL will see that you are thinking in hours rather than days and that it is a midwife thing that is best for baby (how can she say that she thinks her needs are more important!) and that you are not specifically excluding her and will tell her in reasonable time. Of course, you will be planning all along for it to be six or seven hours or a day or two, she is not to know that!
You also need to make sure that in conversation you re-iterate that the waiting area is only for birth partners and that you think your dh got the wrong end of the stick slightly at your antenatal lessons, the visiting hours are from xx to yy for grandparents and friends etc. even if it is not the case - and make sure your dh knows this too, even if it is not the case
could you find out from your MIL about her experiences with her children - she might have had bad experiences with over enthusiastic PIL or nice family only bonding time for the first day that a bit of reminding about will work for you too...
good luck in getting the first day you want with your new baby!