L.
If you would be willing to allow your parents to have your baby at their house over a weekend, perhaps a little 'private time' with him might alleviate their need to see him so often.
If that is not feasible, consider this: this is YOUR baby and YOUR family. You are not responsible for your parents' feelings. Tell your parents that you are so happy that they're excited about their grandson and you are thrilled that they want to be such a big part of his life but that you and your husband feel that you need more family time with just the three of you. Assure your parents that you will send pictures often (perhaps even weekly at first) and then make good on that promise. Also, sit down with them and schedule perhaps 2 weekend visits over the next 12 weeks or 3-4 one day visits. Fall is coming up, so suggest that they come down one day to take him to the zoo or some other outdoor activity. Actually scheduling some time with the baby would set some boundaries and give them something to look forward to.
Good luck!