G.,
As a dog owner and a Mom, I don't think it's fair to expect your parents to remove their dog from their home for your visit. I also don't think it's fair to expect everyone to alter their lives and habits to accomodate your wishes. As for the sleeping, I'm a firm believer that kids will sleep when they are tired. If you stick to the regular nap time/feeding schedule/bed time, I think your son will adjust just fine. Our son has a very regular sleep schedule and he spends the night at my Mom's house one Thursday a month with no issues. My mom keeps him on the same schedule we have and she has 2 cats and 2 Great Danes!
I think having a talk with your parents won't hurt, but don't be surprised or disappointed if you don't get the answer you're expecting. I think you should take it in stride and just enjoy the visit and have your son enjoy spending time with his Grandparents as much as possible. If he gets a little less sleep or wakes up a few times, it's not the end of the world.
We have been contemplating a trip to my Dad's house in Arizona for sometime now. Although there is PLENTY of room in the house to stay, we will be opting for a hotel since the home is not set up to accomodate a young child. Just a thought...
Good luck and have a safe trip.
T.