I spent several breaks at the Longleat Centre Parcs, which I thoroughly enjoyed. The kitchens were well equipped, but it depended on the type of place you chose. I expect there have been updates since I was there, about 10 years ago. I always self-catered, but took as many provisions as possible as the shop on site is expensive and nowhere else locally.
I also went with family, but chose to have separate accommodation. It was lovely spending time with them, but I wanted to give them their own space.
At Longleat you will have to be prepared to do a fair bit of walking to reach the different areas, including some hills, but it helps to fill the day.
I hope you have a great time, leaving you with fond memories.