To not want to go on a 'surprise' forced holiday with MIL and 3 Nephews

Good question, @terracottafarm have you resolved this or will you be condemned to CP again?

this thread popped to mind this morning - I hope you avoided the family holiday gift this year OP!

I actually think that Duty can be very very harmful in some cases.
Duty can mean people put up with a lot of toxic and/or abusive behaviour.

I don't think either SDC or DC see me as a duty, thank goodness. But a sense of duty underpins a love of family, I think. Yes, my family are lovely.

Supportive or dutiful?
I really hope that I am not a "duty" to my DC when they are older, any time spent with my Mum and in laws is was mostly because I actually wanted to.
Family can be important but not all families are equal, yours sounds lovely @Grammarnut but its sadly not the case for all of us so not all of us will go on holiday with these people that we may not like or who are actively awful in some cases.
My sanity and wellbeing trumps duty every time

I am happy for you. But family is important for many people and the connections of blood and marriage underpin the happiness of many. Also, duty is an unfashionable concept, I know, but life sometimes requires we do it.
I am lucky in having a very supportive family. My late DH's children look after me and sustain me. I am their step-mother and never brought them up, having married late DH when his children were adult - and he did not bring them up either, btw. The same applies to my own DC.

This.
I've opted out of family holidays... not my thing- other stuff I'd prefer to do.
Nobody died- nobody went NC.
Just say no.
Its really that simple.

I loathe Center Parcs and don't go away with family at all - I promise I am not lonely and have plenty of substance to my life

I think your dh needs to be upfront with his mother and say that you both don't enjoy these holidays so please don't include you in them anymore.

It will upset your mil. She clearly sees this as a chance to spend quality time with her children and grandchildren. But the only other alternative is to keep going and grin and bare it. Perhaps you can offer a compromise of every other year? Maybe the years between you can take mil somewhere separately without sil family?

I don't understand the dislike of Center Parcs. These places have lots of things adults can enjoy. I wouldn't mind going and would go like a shot if offered this holiday - I would not take my dog (as OP and DP both work presumably they have a dog-walker who can look after the dog whilst they are away?).
Though I am not an advocate of 'be kind' (which tends to get shoved onto women about stuff that impinges on them doing what they want/need/feel safe with) doing what one ought to keep family relationships going is no bad thing. We are not islands, but social creatures. Acting only for one's own pleasure ends up being enervating - there is no substance to your life - and ends up with loneliness.

Gran may be glad of an excuse to shed an annual expectation that could be getting burdensome for her? Try sounding her out.

"She is borderline obsessed with her grandchildren and will get upset..."

I think you have to somehow play on this. Think of a way! Maybe at the same time say you cannot make it, include in your letter/message/email that you would love to have a photo/video chronicle of her grandchildren and were thinking of buying MIL a photo book so that she can create an album to trace every week of their darling lives as they grow up... Obviously, you do not need to ever look at it!

100% this.
There are always a lot of MN posters who say we should go along with what parents/in-laws want, however miserable it makes us (and often our kids) and even if it means using up our precious annual leave to do things we don't want. I do wonder whether these people are such martyrs in their own lives, or just like to push their ideal of "kindness" on to others.

@terracottafarm Did you resolve or have you kicked the can down the road? Sending strength.

I’m astounded at how many people think the OP should suck it up. This is our one rare and precious life. As long as she makes time to see her mil, or at least facilitate her husband seeing her freely, and maintain a reasonable relationship with the nephews, she’s under absolutely no obligation to go on holiday with them every year, to please the mil.

We are allowed to please ourselves too, by avoiding things we just don’t want to do. ‘Family is everything’ doesn’t mean ‘your needs come last’. There is a whole world of interaction between annual Christmas holiday and going no contact. Lots of ways to have a healthy family relationship without doing something you hate every year just because it makes someone else happy.

If the mil is a decent person, she’d be happy with any number of other ways to stay close that the OP is more comfortable with.

Just don't go. Unless you have unlimited money and free time, holidays are a zero sum game-if you do this, you will be missing out on opportunities to do something you would enjoy more.

Maybe the dog will also find his inner child while being tormented by the kids!

Gran chooses the whole thing. The young, child free adult couple don’t have to be there for her to enjoy her GC.

Gran chooses child centred places because of her grandchildren. Grannies are like that. If deciding whose fun should be considered most, the children win hands down, not the adults for one weekend.
My own memories of these weekends.are luminous. In photos she's smiling all the time when helping children feed ducks or build sandcastles or sail boats...As I said before, join in. You might discover your inner child. If not, you,ll still make your make your MIL happy by sharing in the family weekend.

THIS! No one should be having kids just so they can become unpaid carers when they grow up

HOUSE!!!!!!

And you really think care of older people will fall to these three MALE relatives Yep im sure there will be a change in expectation of men once OP is older. 🙄 So now the siblings of the child free are having kids so their siblings will be cared for when they are old. Heard it all now

A few people have said to announce you are ill the day before you are meant to go. Please don’t do this - it just wastes everyone’s money.

It's not impossible just say no
As for the children winding up your dog that's something that could easily go wrong if the dog decides it's had enough and bites.

It's two days and would make your MIL happy. It's not a big deal. Do you really live in such rarified air?

if that is the case then I would not want to collude with piling such a burden on the kids and would deffo stay away