We have a lovely relationship with DH's parents and have really enjoyed holidays with them every other year since our children turned 3 (we couldn't afford it before then). They alternate with SIL and family.
I am pregnant with our 3rd and next year is our 'turn' to holiday with in-laws. We enjoy holidaying alone, too, but the kids absolutely love their grandparents adding an extra dimension to the fun. We asked them about booking something and sent some options and they told DH they won't go abroad with us if we have a baby, or even an under 3, because they didn't when they had their children.
So we won't be holidaying with them for the next 4 years, which means our children will be missing out on time with their grandparents while they are young.
They will still go away with SIL in the meantime, and they have a much closer relationship with her children anyway, so I feel this is another way that our children miss out with them.
I don't really understand what they have against babies. I find babies easier than 3-year-olds (ours will be 7 months by the time the holiday comes around.) We will look after our own baby, who will be breastfed like the others, so will always be with me and we don't have to worry about sterilising or making up bottles etc, not that it would be their responsibility if we did. We do BLW so baby will just eat what we eat, and we are looking at the Canaries, which isn't exactly primitive - they sell nappies and everything! We will have separate apartments, so they won't be disturbed at night, and we don't ask them to do any babysitting while away (last time they offered and looked after the kids for a couple of hours once while we went for a drink, that is it and we didn't ask or expect even that, we wanted to all spend time together.)
I don't understand how us having a baby will impact on them. It will be our responsibility. They have 4 holidays a year, two of which are to very luxury locations, and they usually enjoy their holidays with the grandkids in contrast. So this wouldn't be their only chance for a break or anything.
Are they being weird or am I wrong to feel insulted that they think our baby would ruin their holiday enough that they won't entertain the idea and miss out on time with their other two grandchildren for years to come?