Hi Jane, I joined a couple of weeks ago and paid £5 membership (think this is a special offer for Jan/Feb). The four weeks off thing is if you give the consultant notice you will not be at class that week, otherwise if you took a week off when you went back you would be expected to pay for the week that you were off.
So far I've found the food very easily adaptable to children (I have two DSs, aged 2 and 6). We have pasta a lot and I just add more cheese to the children's portions, you can have things like roast chicken, baked potatoes (butter and extra cheese for the kids), homemade soup, etc, etc. Bread, fruit and full-fat yoghurts are generally always on offer in our house plus the odd chocolate treat. Many recipes can be easily adapted using spray oil or taking olive oil as a healthy extra. TBH I have found this far easier than the WW points I was following before, I found it very difficult to find family meals that didn't obliterate most of my points, therefor I ended up making separate meals for myself three or four evenings a week.