How many times have you seen them OP? You say at the hospital and ‘brief visits’ to their home. So at least 2-3 times in less than 3 weeks? I think that’s quite normal. As pp’s have said, it’s good that they aren’t struggling! And they have likely taken him away to show him off to other people. My mother expected to be seeing us every few days but between my family, dps family and all of our friends we had lots of visitors and we needed our own space as well. Both my mother and mother in law expected to be very hands-on and helping out as well, but between me and DH we didn’t need that, I know they felt a bit put out but we really didn’t need help and were both very excited to be looking after the baby. It really is a good thing if they aren’t needing help, even with household things.
I’m sure that you will see him but remember, even though you are the grandparent there will be lots of other people wanting to see him, and lots of friends that they will want to show him off too.
As for not visiting your house, might there be a reason for that? DPs father smokes so we didn’t take DD to their house until after she turned one, and then only on the agreement that FIL wouldn’t smoke in the house that morning. And my parents have not very well trained dogs, so I didn’t take DD there for months, until I was a bit more confident. If there seems to be no reason then just give it time, they will bring him round at some point. But in the newborn stage it’s much easier to have people visit you, where all babies things are.