NC for this as potentially quite outing.
DH has a very small family. Him, his mum and dad and his uncle (mum's brother). No grandparents, siblings, cousins. There are some great aunts and second cousins he doesn't know, that's it.
FIL doesn't like the uncle. At all. As he has no other close relatives, the uncle stays with MIL and FIL for family type occasions (at MIL's invitation), like Christmas and Easter. FIL doesn't really speak to the uncle and complains about him behind his back the whole time. There's no obvious reason for FIL's dislike other than that he's a bit of a curmudgeonly old goat at times, and he perhaps feels that the uncle is taking the piss by visiting all the time and not really giving anything back in terms of hospitality (the uncle has all their food and drink and doesn't contribute or buy them a meal ever). But we don't know the uncle's financial situation and I suspect he doesn't have much spare cash.
MIL and DH both like the uncle, I've got nothing against him, he seems harmless and good-natured.
So... are DH and I bring unreasonable to name our baby DS after the uncle? It would be a middle name, not first name. The middle name works perfectly with our chosen first name and surname, and we have a family tradition of giving a middle name from someone in an older generation. FIL will totally hate it though!