We were out for MILs birthday this evening, just me DH & our children with MIL & FIL, having not been invited for the umpteenth time (we always used to do these things together until they separated off) to the earlier meal with BIL & SIL so we arranged our own thing, and as soon as we sat down MIL reads out a text from SIL saying 'Say hello for us to Snobbly, Husband and kids - tell them we miss them.'
I spoke to SIL on Wednesday.
My last text to her was suggesting we meet up after our holiday - we leave this week so no time beforehand. Said we're free any weekend next month and to that I received a thumbs up. Nothing since which is fine, she might need to check stuff, and if it happens it happens.
Admittedly we haven't seen them in a while but we've never socialised and they make as little effort in that respect as we do -in fact for the majority of the time (18 years) we've been told how much BIL hates kids (now teenagers) so we've never felt that comfortable initiating casual get togethers. We just never developed the habit so as a by product of that we have a very 'basic package' relationship with them.
The delivery of this via MIL made it seem like we are these meanies who ignore them when it's always been like this. The kids don't know them that well so to say she 'misses' them seems disingenuous to me.
My face was puzzled and I just said - but we spoke last week 
For context SIL is married to my husbands brother. I just don't get this sudden gush of missing us - she didn't say she missed us on Wednesday.