Wow. Your FIL walked in while you were naked. PLEASE tell me he walked right out! I would have been so upset that it would have affected my ability to birth my child. That is beyond the pale. They didn't even knock? The woman didn't walk in first to make sure you were decent?
I have to wonder what on earth is wrong with your husband that he doesn't "get it". He's not the one having the baby. I don't care if it IS cultural. You get to decide who walks in your labor/delivery room. NOT HIM.
I'm glad that you have talked to them now and they are in agreement to wait. I'll just bet that this has something to do with their work schedule being made easier and the fact that it's your 3rd baby and the excitement has worn off some. Problem solved? No, not really. Your husband STILL doesn't get the boundary issue.
You had better put your foot down and tell your husband that you will NOT wait hand and foot on his parents when they come. You will NOT cook for them. It will be his job to deal with them about this issue. They should be cooking for you - you just gave birth!! Just tell them flat out that you have to rest and you cannot cook for them. And turn around and go lay back down. Don't clean up after them. DON'T CLEAN! If they leave a mess, tell your husband to clean it up.
Honestly, I'm just astonished that you put up with this with 2 other kids. What were you thinking? You are supposed to rest and heal after childbirth, not take care of people who are really only there to look at the new baby and take your husband away from you so that you're alone with a newborn and a toddler.
It doesn't matter if they are offended, KW. Your husband should be caring about offending YOU, for heaven's sake! If all he cares about is offending his family, then he is short-shrifting the mother of his children and his wife. He doesn't get to do that - you come BEFORE his parents. NO COOKING FOR THEM. NO CLEANING UP AFTER THEM. NO LEAVING YOU ALONE WITH 3 CHILDREN to "hang out" with them.
Good grief. I'm sorry, but your husband is nuts and it must just have been baby hormones that let you think that you had to allow this.
Take the bull by the horns. You tell the doctor and nurse who can and can not come to the hospital. NOW you know that you cannot make assumptions about your parents-in-law. No matter what they say in advance about coming a few weeks later, you tell the hospital personnel what you want - they do NOT mind being "the bad guys". Tell your husband point blank when you go into labor that you will not have his parents in your hospital room. Be a bear if you have to. Don't back down. Say to your husband "I WILL NOT HAVE YOUR FATHER SEEING ME NAKED AGAIN!" That way when they tell him "Oh, we've decided that we want to come", he won't say "It's okay" because he knows you'll be a laboring monster to him if he tries this stunt.
Don't be a pushover. And don't apologize for feeling the way you do. YOU have a culture too. Your culture matters. And since you're having this baby, your culture and feelings and wishes trump your husband's and his family's.
(Wanting you to cook after giving birth - I'm seething for you...)