I used to get my own DMum to talk to MIL, saying things like 'We are so excited about the birth, but we'll only go and see the baby when we are invited.' and 'don't you remember how hard it was having to entertain family whilst juggling with a newborn?' It didn't stop them entirely (both DParents and PILs live a five minute drive away from us so no escape) but I think it calmed them down a bit.
DP's role is to support you in this whilst you support your baby. Get him to be your gatekeeper. If they turn up and it's not suitable, he can answer the door and tell them whatever he wants until they get the message and stop coming round uninvited. If you're there on your own and they try it, don't let them in, and get DP to talk to them about why you were hiding behind the nets didn't answer the door.
If they aren't going to realise what a nuisance they will be on their own, they may have to have it spelt out to them. They will be cross now, but as soon as they hold their first grandchild for the first time (whenever that is) they will forget they ever were. You, on the other hand, as other posters have said, will resent them for years if they take this special time away from you. I do. I am still rebuilding my relationship with PILs following what for me ended up being a very traumatic post-birth experience which they did nothing to ameliorate.
You could also get DP to remind them that a newborn does nothing but sleep, poo, feed, cry, sometimes all at once, and that they might have a better bonding experience with it if they wait until it is a few weeks old. How can they expect to be able to take it out in the buggy if it needs it's mother every few minutes, after all? They could be around for the first smile instead or better yet, the first steps and they'd get a lot more out of their visit.
Bottom line: your baby, your rules. Just because it's no longer inside your body doesn't mean this stops being the case.