Pedal powered family transport?

[flecc]

One of those attached to a tandem? Or a sturdy DIY bike trailer like yours made using aluminium ladders perhaps, but with seats? Insurance would still probably be a problem.

There has been the odd tag-along tandem at times, for two different size kids, the last one without pedals. Another variant tag-along has an additional front carry-only seat for a toddler, mounted on the linking tube just over any rear carrier position.
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[guerney]

There don't appear to be many modern passenger trailers suitable for older children and adults.

https://freedomforkids.co.uk/shop/special-needs-bikes-trailers-cycling-seats-disabled-children/wike-xl-bike-trailer-special-needs/

 

[StuartsProjects]

There don't appear to be many modern passenger trailers suitable for older children and adults.

You can still get the batteries for that, look see these on eBay, still sealed in the bag;

 

[guerney]

Probably not what the OP is looking for but... a couple more adult passenger trailers, but single seat.

Adult Carrier - 32" Sloped - Solid Fabric - Bicycling

The "adult" trailer is a bicycle trailer for special use needs often for mobility impaired individuals. The frame is 8" longer than our standard frame. The superstructure is 32" high so that a 6 ft tall individual may sit with his or her legs contained within the frame or extended over the...

equinoxtrailers.com

Special Needs - Large - Stocked in Europe

Expand the horizons of your loved ones with special needs. This large bicycle trailer folds for easy transport and storage.

wicycle.com

Bicycle Trailers by Blue Sky Cycle Carts

Home page for the Blue Sky Cycle Carts, great for all cargo: Grocery shopping, Picnicking, Camping , Cross country touring, Deliveries, Pet carriers

blueskycyclecarts.com

 

[chris667]

Something like this?

Thorn Me 'n' U2 Childback Triplet - Yellow | Thorn Tandems & Triplets | SJS Cycles

For the full range of high quality steel framed touring bikes and tandems please click here to visit the Thorn Cycles website (note: clicking the link will open a new browser window). We recommend that this item is collected in person. If delivery is absolutely necessary, the bike will be...

www.sjscycles.co.uk

You could always add a motor somewhere. They come up for sale sometimes as kids outgrow them. Being a Thorn, they are quality and will hold their value for the next kids.

Historically people have done similar things with 20" wheel shopper type bikes - it would not be a terrible fabrication job to make a three seater!