We arranged to go to them on the 27th. Usually we would go home for New Year, as DH's family tend to do their own thing.
We saw them about three weeks ago. MIL asked if we would consider coming for New Year - 'come for', not 'stay until', which I thought significant. I said I thought we had arranged to arrive the 27th. She said we had. DH said he would prefer to come on the 27th, to see relative who is leaving on 29th, but would love to stay until 2nd, and see different relative who will be there for New Year. MIL seemed very happy with this, but I felt a bit awkward, and thought that she maybe wanted us to not come until the 31st. DH reassured me this was not the case. It would be odd, because MIL usually loves us all to stay as long as possible, so it feels quite out of character.
Then we saw them again last weekend. I said 'See you on the 27th' as we left, and she denied all knowledge of this arrangement, although again said she was very happy with it.
AIBU to think she wants us to not arrive until later for some reason? It is tricky because DH wants to see both relatives, and there's not really another option for this other than staying with them.