When my daughter was 4 or 5, she and I went on holiday with my oldest brother and his wife for a week. I barely got a look-in with my own child, because my brother was thoroughly enjoying being her uncle and helping her explore where we were. I and my SIL lay by the pool, and meandered along the beach by ourselves. My daughter had a whale of a time with her doting uncle, and got to do a lot more fun things as a result. They didn't have any children at that point, but even if they had, I suspect he would have done his utmost to give me a break from being a single-parent (with my ex, but might just as well not have been as he was still into the life of a single lad...), regardless.
Fast-forward a good few years to when my ex and I had split for the last time, my daughter was 13 and my son was 5. We went to Spain with my parents. First time either of my children had flown - both were nervous about it (and my daughter to the point of a panic attack). I dealt with all of this alone, whilst my parents pretended not to know us. I remember thinking at the airport, that the holiday could only get better from that point on...
We got to Spain, only to discover that my parents refused to do anything out of their routine... and we were expected to fit in. I did all of the donkey-work of two children completely out of their comfort zones, one still young enough to expect his own routines of bedtime, etc., to be observed - and who was missing his Dad, due to the recent split, and the other argumentative and hormonal. My son stopped sleeping. But, actually, as there was no bed for him to sleep in when we arrived, that's hardly unexpected. My parents expected me to sleep in a twin-sized bed... with two children, both of whom slept in their own rooms, in their own beds. Nope. Not happening. My children like to move in their sleep! So my son was on the sofa cushions on the floor... which he thought was very exciting, and promptly stopped sleeping. My father moaned that he couldn't "nap" on the sofa in the evenings, whilst listening to the TV (ie, completely dominating the room, as he snores whilst he "naps"). There were, incidentally, armchairs - or his bed, in his room. But nope. He wanted the sofa, because he lies on the sofa in his den at home (my mother has a separate space for herself to sit in during the evenings, at home). My mother was bitchy about having to share a single living space with four other people in an evening. My daughter and I were very "WTAF?!" about that situation. Did they expect us to sit in our bedroom, by ourselves, every evening?! Whilst my son pretended to go to sleep on his bed of sofa cushions directly next to our bed?!
It was hot. My parents expected us to walk for miles every day between the town their villa was in, and the next one over, purely so that they could buy cigarettes (I don't smoke and didn't appreciate clouds of it wafting around my children). We had to eat in the English ex-pat restaurants, which disappointed my daughter who had been hoping to eat Spanish food, not greasily fried egg and chips every day. I tried to order a coffee, once, in one of them, only for my mother to over-ride me and say "she'll have a coke like the children" (when she knew that they drank water or juice at home...). But I didn't want to start a row, knowing from experience that my mother would turn it into a vendetta of agonising silent treatment - and I wanted to protect my children from that awkwardness and/or her doing the same to them. So I drank a coke through gritted teeth. Whenever I tried to suggest the children and I did something alone (even if just to go to the beach which we could see from their villa), nope; my parents kicked off. We had to stay with them. 24/7. We didn't get to set foot on the beach even once. My son was bitterly disappointed, but every time I said we were off to the beach... there was an argument, and guilt-trips from my mother.
So I bit my tongue until the last day, when I was ratty from exhaustion - and I demanded to know why the fuck they'd invited us, and made it sound like it was going to be a fantastic break for all of us. Why they'd promised my children a trip to the nearby zoo (never materialised), and bragged about the beach we could literally see from the villa windows in a way which made it seem like we'd be spending at least part of one single day there. "Well, we thought you'd like it!", they said. Like it? Nope. I had spent a small fortune on our tickets, which as a single mother, I actually could have found better things to spend the money on... for exhausted, bad-tempered, bored children with belly upsets from all the greasily fried foods my parents ordered for all of us without asking us if we wanted to eat it, and then insisting that we had to, rather than waste the food!!! And then, the kicker:
"We thought you could do with the break!!!"
I'd have had more of a break if we'd stayed at home. My daughter would have been able to go out with her mates, and my son wouldn't have been out of the routines which all small children may not revel in... but actually need. I also would have been able to find little pockets of time where I could have sat on a sofa in an evening, had coffee to drink as/when needed, and slept... without being kicked by a gangly 13 year old, unused to sharing a bed with her mother, circumnavigating it in her sleep (yes; I ended up with her foot in my face at several points during that holiday - and was black and blue from being kicked!), recharged my own introvert batteries.
Never again will I go on a family holiday. I won't even holiday with my daughter anymore. She goes off alone, or with friends - and I wonder how much of that is because she remembers the miserable time we all had in Spain.
The lesson I learned, though? My brother is 14 years older than I am, and spent his teen/young adult years pretty much raising me whilst our mother and my father suited themselves. My parents... have always put their needs, their wants before mine, let alone their grandchildren's. 
And that's why there's such a marked contrast between the holidays...
Don't bite your tongue. But be prepared for their responses to be unsympathetic to your own emotions/feelings/confusion. They've undoubtedly had a great time - and will have presumed that your family will have experienced the same. Good luck.