I'd say that, at least for the children, Switzerland represents a large chunk of their growing-up-years (and their connection to friends). Even if they, each individually or with you as a family, leave Switzerland, they might one day yearn to return to the place they knew when they were young. What a pity if that were not possible! Especially since you are already so close to being able to naturalise. I do hope that you, as the parent(s), can speak German, too.
Suppose your children live here till they each turn 18 or 20, then go abroad (= outside of Switzerland) to study, travel and work, and later choose to return when they are parents themselves. They'll be 30 or 40 by then. About then, you retire.
What would happen if, say, after your children had flown, you also returned to the UK and then, just when they're in that phase of nest-building for their own children, you begin to get old. It would be a great pity if you and they did not all have the same citizenships so that you could all - should you want to - live in the same country. If your children were Swiss, and if they chose to invite you to stay with them when you are old but you were NOT Swiss, they might end up having to make financial support pledges (guarantees to the Swiss government that they would always cover all of your costs) for you, which would be entirely unnecessary were you already Swiss, too.
If you have ageing parents of your own, who are not living in Switzerland, perhaps you already feel that pull between "here" and "there", and a certain uncertainty or even worry about their future and your responsibility (if you feel you have one) towards their care as they grow older. Or even if they are healthy wherever they live now, you, they, or your children might be wishing they could join into your lives as grandparents.
If you and your children all naturalise as Swiss as soon as you are eligible, you will be doing your children the favour of preventing their having that same tension - at least as far as the papers are concerned - when they are middle-aged.
In particular, before summer, about your 18-year-old: please, make sure that she/he does not de-register from Switzerland before you've thought through everything about naturalisation. She/he is an adult, now, and will not automatically simply be allowed to come back to live in Switzerland based on the fact that you and the younger siblings live here. As far as I understand it, she/he will be evaluated newly, on own standards, like any other single UK adult, i.e. always allowed to enter Switzerland, but needing an own permit to live here, based on employment, etc.
Disadvantages of naturalising as Swiss?
- You'll need to set aside some time to prepare.
- Collect all the documents.
- Have your finances in good order.
- The UK and Switzerland both allow dual nationality. If you have other citizenships besides UK, you'd need to check whether that country or those countries allow dual (or multiple) nationality and, if not, consider whether or not you (and each member of your family) would be willing to forego that/those other citizenship(s).
- Depending on the Gemeinde in which you live, you will have to learn more or less of Swiss history, geography and politics, and pass a written or oral exam in these topics, in German.
- And the fees, of course.
Altogether, you'll have to add up theses costs, financial and other, and decide whether these feel unreasonable, or a relatively small price to pay for the priviledge of knowing that you and your children can all live, freely, as you choose, in not only the UK but also in Switzerland. To me, it seems one should maximise flexibility since we live in a very strange world changing in ways we cannot fully anticipate.