I'm going to try to be as simple as possible here.
Grand parents booked a cruise for summer 2025 and offer to take their eldest grandchild who will be 4 and offer the same to their nephew who will be 6. Both children play together occasionally and get on great at the grand parents house and aunties house, but don't spend a huge amount of time together else where. At 4 and 6 this means both kids will be eligible for the kids clubs within the same group and old enough to understand why they are not with their mum and dad at home.
Also , the nan's younger sister is going and taking her two children who will be 9 and 12. So lots of cousins having fun and help on hand to watch the younger ones. The parents of the grand child were 100% fine with this trip with grand parents despite initially being put out that the grand parents would not pay for them and the two other grand children to go on the same trip.
But something has been lost in translation and the parent has just realised 4 months on that the 6yo cousin is going (this was never hidden and has been openly discussed but the mum was pregnant and not sleeping well so may well have forgotten) and has expressed their unhappiness. They feel the grandparents should be taking their other grand child instead, who will be 3 at the time.
The grand parents have said they do not feel able to look after a 3 and a 4 year old for an entire week but will happily take both the children away for a week the following year and then the year after that take all 3 grand children away. ( she has 3 kids under age 3 ).
The grand parents are also planning on buying a motor home for retirement in 5 years, specifically to take the children travelling, as they will be old enough then to go for as long as they/the parents feel comfortable. Only adding this to show the GPs have every intention of spending some holidays with all the grand children every single year as soon as they are old enough. This trip is NOT a one off.
Anyway, now the parent has said her child is not allowed to go on the holiday as the grand parents are taking the nephew instead of the middle grand child. The grand parents have said they will not be forced into taking a child they don't feel they can safely care for , especially as he wouldn't be in the same kids club as his brother.
Who is being unreasonable?