I'm 59. I battled the lower back problem, but it finally cleared up after about 10 years. Assuming there isn't an extruded disk, I'd suggest trying 2 Ibuprophen 3 times a day for about 10 days. Do not do any exercise at all for these 10 days. It may cure the back issues.
Try to keep your pack under 30 pounds. Otherwise lifting it to put it on may bring back the back problems. Carrying it may also cause problems.
Be careful about creating other family issues. Backpacking can be expensive starting out. It can also be time consuming. Hiking coupled with simple car camping is a lot cheaper.
There is a growing trend among kids to spend less time on computers. You may be surprised at their interest. They may be open to easier hikes or car camping for just one night. From there they may get interested in backpacking. If they have smart phones, I recommend letting them bring them. Kids like to send pictures from the trail. A lot of adults like to update blogs from the trail.
Avoiding injuries is very important. Personally, I don't do anything that causes serious pain or fatigue. I'm not a big believer in pushing through pain as it can lead to chronic conditions.