My DH and I are now home after spending a couple of weeks on a narrow boat. I agree with some of the comments about chosing your companions carefully. Earlier this year we were joined by another couple for a few days. I was truly glad when they left us in peace although we had a few laughs with them. However, when our DC were younger, we had such a lot of fun as a family.
There is very little space on a narrow boat but you will need a complete change of clothes and prepare for sun, rain and cold. Other GNs have advised you to plan your days around trips to pubs for eating but we tend to moor up in interesting places (tow path side of canal) that we see as we go along and eat in (basic, simple food, accompanied by wine, beer or cider - much better than the huge, over-seasoned meals that most pubs just plonk down in front of you). TV, radio and mobile reception are flaky, you can't rely on them at all for entertainment.
Doesn't sound too good so far, does it? However, there is a lot to enjoy if you are all reasonably fit and willing to make an effort to work together. I regularly swap with DH, steering the boat and working the locks. Locks can be hard work but are also where you chat to other boaters, find out what is going on and get all sorts of snippets of information. I sit at the back with DH when he is steering. Because the back of a narrow boat is quite high, we have views over the countryside and the water, wildlife and other boaters provide us with constant entertainment. If there are more than two of you, a 'cruiser stern' provides more room for company.
Oh, you can turn narrowboats around other than in a basin. Look on the maps for 'Winding (holes)', they are often placed close to lock flights and are areas provided for boats to 'wind', the maps show the maximum length of boat that can turn, usually 70 feet.
The Ashby Canal has 22 miles of lock-free cruising, that may be a good starting point.
I think narrow boating on UK canals is a bit of a 'marmite' experience, you may love it or hate it. DH and I have enjoyed it for many years and go out in all seasons. We own a share in our boat.