Yes, I know I'll probly get the rolling eyes for this...but, Samantha came home to us at 9 months.
We spent the first 6 months pretty much just immediate family. One year later my parents watched her at our home for 12 days. (she was 1.8 months old). They have had many overnights with her at our house. That's a great way to have the little ones realize mom and dad are coming back, it's their house! Between age three and four she has now spent up to four night at their house. At least four phone calls a day just to let her say what she needs to! It's your in-laws and parents, and just as they said, he was having a great time.
If your able, drop him off later in the afternoon and pick him up in the morning at breakfast.