Welcome to the forum Vivi.
Be careful with that Lafree, stolen bikes don't have keys and chargers of course! I don't believe the "office clearance" for one moment.
The Lafree can be a good towing bike, but only if it's a Comfort model with 5 or 7 speed gear hub. The standard 3 speed bike with it's 43" low gear is too high geared for towing in very hilly territory. The motor system isn't a powerful one, and with two children on tow you'd still have to work quite hard, and very hard indeed on the steepest Bristol hills. I own a 5 speed Twist and manage 14% hills with a large empty trailer, but when it's loaded, about 10% to 12% is the limit, and it's still quite hard work.
Spares and service are a very real problem now that they've been discontinued, Giant no longer interested in giving support. They still have batteries at a high price of £250, and chargers at £120, though I have another source for chargers at around £45. The motor sprockets which wear a lot are no longer available, so all in all, a second hand purchase is increasingly risky.
The only bikes I can think of that are around your price bracket and very powerful hill climbers are the Powabykes. They trade through local dealers normally, and there are some in your area. If you click the link I'm giving, you'll see two Powabyke dealers at four Bristol locations, and hopefully at least one can let you have a test ride.
Bristol Dealers
One is an approved service centre.
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