Good job on highlights. I know only too well what you mean by age issues.
Southern End- Do you mean the Old Fort Trail at Jasper. I'm not familiar with one at Banff. 2,3, & 4 or 6 could easily be done in one day. My preference would be the Jasper cable car, if only doing one, as it is more open up top. Johnson's canyon is on the old road to Lake Louise, but doing it while travelling would really curtail other activities.
Middle- 3 & 4 plus a visit to Emerald Lake & the natural bridge would make a nice day trip. There is, or was, a salt lick in the Natural Bridge area that wildlife frequented.
There are 2 tea houses. Lake Agnes and Plain of 6 Glaciers. 6G is a much longer trail starting with the lake walk (flat) then climbing. I think 13-14 Km round trip. LA probably about half of that, steep but nothing technical at all on either. From the shore of LL in front of the chateau look up to your right, 1-2 o'clock and you should see the roof of the LA tea house in a mountain
valley.
I'm not sure how much parking there is at the Paradise Valley trail head. You may need to arrive early. Also check with the rangers as they may require groups of 5-6 on that trail.
5&6 you will visit while going to Jasper.
North end - 3 & Old Fort Point and Jasper Park Lodge area would be a nice day. 1,2 & 4 another day. There is some easy hiking around Angel Glacier which I recall being quite pleasant.
If you are in Banff around dusk and not too exhausted from your days activities maybe head down to the Vermilion Lakes ares just west of town. You might spot some wildlife as they tend to emerge around dusk.
Hope this is some benefit.