Nat's mom is quite full-on too, but you should try and explain that at least the first couple of weeks you really need time to bond with your baby as it's the most important time. I was told today that skin-to-skin right after birth should be done a few times in the first couple of weeks, as the baby feels comfortable there and it's good for bonding.
Regardless of how you feed, but especially if you're breastfeeding, you need to be with your baby in the early days. If they want to help with baby things, explain you'd prefer them to *help you* to help baby, so do things that'll help you out like making you lunch, doing the washing etc.. or looking after the little one for an hour or so while you have a bath, but you should make it clear the baby is in *your* care.
I'm not looking forward to telling OH's mom these things either, but it's the first few weeks of your new baby's life with you, and you can't get that time back. Offer them jobs they can do to make them feel like they are helping, as you'll be very tired, but don't let them take control as it just isn't fair.