Ok so when you write a post it makes sense in your head but May be it doesn't make as much sense to the readers.
Firstly we haven't been abroad before, next year will be our first time as a 6 (not even been as a 4 or 5 ) which we are all really looking forward to. With regards to being tied to school holidays, my eldest goes to school next year so all holidays will have to be in school hols. The caravan trips, overnight stays and day trips as a 6 have all been in school hols but they're nowhere near as expensive as a holiday abroad. And I'm always on the look out for offers / vouchers etc. As my 2 are quite young most things have been geared towards the elder 2, but my DC are now coming to ages where they can enjoy activities etc.
To the PP who asked about doing days out etc in term time therefore without SC. Yes we have done it, however, it is very much frowned upon by SC mum and she believes it is wrong. However, that is a whole other thread and not the point of this one. Hence why I think if we booked a holiday at the same time as she took the children away, she would say it would be deliberate to avoid them coming with us. Not in the positive way it could be, but she would use it against us ti the children. Which we don't want.
Also our holiday next year is in spring half term and not summer hols so it is cheaper.
I don't want expensive/ luxury holidays every year just a nice treat to look forward to whatever and whenever it May be. I was merely thinking (probably way too far!!) In advance about the year after and looking at the prices for package all inclusive hols in the summer hols. But I readily accept what is out of my budget and would not book something I could not afford. I was thinking all inclusive was a good option so the kids can go and help themselves to drinks, ice cream and snacks etc without having to worry about a budget for it. Also whilst my 2 DC and one of my SC will eat practically anything 1 is far far pickier. That way I was thinking they could try lots of different things but always go back to the staples if they didn't like it. However, if anybody has other suggestions of what works well I'm all ears. Also I cook, wash and clean 7 days a week was also thinking it would be a break for me too 
In addition I was thinking that a hotel type accommodation would also provide us with activities and some entertainment.
I was genuinely wondering how larger families blended or not sort their holidays and looking for any advice. Hence I've ordered a eurocamp brochure today! I like that they will also help you with travel arrangements and there looks to be some amazing destinations. Anybody have any recommendations or places to avoid ?
I'm also willing to stay in the UK, we don't have to go abroad it's just I was looking at genuinely quite shocked at the cost of some holidays.
I think I would panic and worry about booking all elements of a holiday separately ie if i book accommodation on specific dates, what if i then cant get flights ?? Or make suitable travel arrangements. I am a bit of a worrier but I suppose I may have to learn if this option is better than going through an agent.
As for what my SC do with their mum, that is nothing to do with us quite rightly. Although as stated earlier she feels she has the right to have an opinion on what days out we may do as a 4. And no these have never impacted on the SC contact time with us.
Thanks to everyone with suggestions for different types of holidays for me to look into - think I'll need a holiday after all the organising and planning !!