Long time lurker here.
Our first bike tour with children was on the Sunshine Coast north of Vancouver B.C.; our first child was 5 months old then. Never known for packing light, I had the trailer stuffed with kids gear and everything else imaginable. Let's just say it was painful taking the first steep hill off the ferry; I was pretty fit then and still the grind was one of the worst I can ever recall. By the time our youngest had his first tour at about 9 months we weren't new parents any more and the tonnage carried dropped accordingly. He joined his 2 1/2 year old brother for that first trip to hilly Galiano Island. The two of them occupied the trailer for another year or so until our next piece of gear - the Burley Piccolo - gave us more freedom.
As the kids grew bigger we knew the trailer would need to service luggage not children. That and a desire to get rid of a second car drove us to consider a tandem. A Seattle builder, Dennis Bushnell, crafted us a custom tandem built with a short seat tube, sized such that a 5 or 6 year old could reach the standard stoker crank but also such that my 5' 2" wife could stoke comfortably with a switch in seat and seat post. This along with the Burley Piccolo trailer bike became the family station wagon of sorts and we did sell the second car we'd owned then and are still a one car family and work at keeping it parked.
Typically we'd tour with one or the other of us pulling the children or trailer. This combo got us quite a few years down the road to where our eldest started riding his own bike on a number of trips. Depending on the road or trails we are on, we found 60K (40 miles) for a 9 year old perfectly doable, particularly if there are ample ice cream stops along the way. Now at 10 and 13 there is sometimes a discussion as to whether we take the tandem or not - usually because one or the other enjoys going *really* fast (compared to what they can do on their own). Most every year myself and one of our kids ride the tandem from our front doorstep to one of the ferries (30 - 40km away) and off to a camping adventure on one or more of the Gulf Islands, sometimes meeting up with the rest of the family or a group camp adventure. Trips that start at the doorstep are my personal favourite. We are soon heading out for a 5 day trip although this one we are leaving tents behind to enjoy something of a pleasure cruise to Victoria and a comfy hotel from which we'll head on our singles to explore the southern tip of Vancouver Island, Sooke and such.
We could have done without the tandem and simply adjusted our routes and expectations, using the Piccolo for the youngest and having the eldest start to ride a little earlier. But I don't regret getting our tandem built as it has opened up possibilities and remains a great date machine for my wife and I.
Having suffered from some back issues myself, all of which I can solve with appropriate core strengthening (which I sometimes forget during the good times), I hope your husband is able to recover and re-join in the fun. In the meantime you've got support so take advantage of it and just get out there!