My childhood was as you describe OP.
Every holiday my maternal GP's would pitch up and stay for as long as possible.
I'll be honest, as a young child I loved it.
However, as I got older (and more independent) I really started to resent every holiday being dominated by their presence.
As much as I loved them, as they grew older it became increasingly difficult to not feel frustrated by how their needs stifled any activity my DP's and I might have wanted to do, or my feelings of guilt going out with friends etc as my GP's were visiting.
All that said, it was nothing compared to the strain it put on my (full time working) DM who had to use her holiday to cater for them.
I'm sure there was a trade off when I was little in terms of childcare, but later on it was akin to being a full time care assistant with GP's expecting every whim to be fulfilled - tea on demand, their programs on the TV, only the food they liked, trips out to places they wanted to go etc etc.
It drove my DF round the bend and his response was to absent himself as much as possible when they were there after his attempts to persuade DM she needed to limit these visits in both frequency and duration failed repeatedly.
So from my POV I also lost out on time with my DF.
My DM was an only child and I'm sure this was a major factor. She felt guilty that they had nowhere else to visit and my GP's played heavily on this.
She's admitted since that she wishes she'd never got into the "pattern" they did - one she was resentful of and did impact her feelings towards her parents.
The situation resolved itself when my GP's died within a few months of each other. I was 15 at the time.
I was sad at their passing but I can also say the following Christmas holiday with my DP's was the best I'd ever remembered. Totally relaxed, happy, eating food we liked, doing activities we wanted and my DM not being run ragged after hosting for 2 weeks (being expected to cook a full English breakfast every day, lunch and "proper" dinner).
Sorry for the long post, but what I'm trying to say is that the ripples do move fast and far from an issue like this. Your children might not say anything (I didn't) but don't assume they are happy with how things are and it would be sad if the resolution to the issue was the same as occurred in my family.