Every inlaw/grandparent has their own obsession. My dad's is that I don't give her enough water. FIL's is that she should be wearing shoes indoors. MIL's is that she's too cold. Just smile and nod and ignore.

what else can they ask about to make conversation? He doesn't eat any variety, doesn't get around, has no interests, does no tricks . . .

Grandparents get weird when there is a new baby. Give it time.

My MIL is also obsessed with sleep - even before I was pregnant. Every visit - her house or mine - every day starts with the following exchange:

MIL - how did you sleep?
Me - fine
MIL - you look tired
Me - I'm not wearing make up

Later that day
MIL - oh! Did you take a nap?
Me - I put on makeup

I think because she and her daughters don't genetically have bags / dark circles under their eyes unless they've been up for days, she has trouble figuring out that this is just the way my face is. I started covering my circles in 7th grade.

OP, not to bring up your favorite subject, but you are sleep deprived. Things are going to enrage you right now that normally you would laugh about. Take my word for it. These few months of infancy are incredibly stressful. Everything will piss you off.