Just divide and conquer.
Tesco "Click and Collect". A really excellent idea. But you don't all need to go. In fact only one of you needs to go - after you've all found the site - and if it's become a family drama, go yourself. Because next holiday you can assign that to someone else. It's simple and straightforward and non-stressful.
And if it's a stressful family day, pause to have a cuppa at Costa.
Checking in at site. A really excellent idea. But you all don't need to go. In fact only one of you needs to go collect the keys and the maps and the events and activities.
Awareness. It's never a question of all chalets or caravans are ready at 4pm. It's a question of the oeverwhelming majority will be ready at 4pm, plus those who pay a premium for early check-in. But some of you are left hanging.
There will always be a family friendly pub/cafe for those with kids whose accommodation is not ready.
You're probably better off taking or walk or hoping that the Tesco "click and collect" person brings back the beer soon. And crisp like snacks.
You will probably have to book a day in advance for pools and activities. So get settled day 1 with late check in, don't get frustrated. Check out their evening activities online the week before you leave.
If you want to make day 1 important - we always stop somewhere local attraction - museum, marwells, animal petting, beach, historical prison, new forest, caves, etc - UK attraction, on route to holiday site.
Make your Day 1, settling in. Let the kids explore the site, but keep an eye on them. Go out for groceries. Make your plans for activities, once you're all unpacked and chilled.
But most importantly of all - Look at your family and judge them.
You need your most capable and practical person to lead to the on-site accommodation - and check out how to turn heating on/off and hot water on/off, and how the tv, wifi and shower works.
You need your next most capable family member to go out and find the tesco click and collect and bring back the food and drink,
You need your least capable person to go check in and collect keys and maps. That's the place you'll all go for questions during your holiday. They're used to the same family going back and back and asking many different questions.
And have fun!
Just don't get stressed on day one. Get settled and keep the kids and adults in good humour.