Itinerary Help

No. I'm assuming by "KS hike" you mean Mannlichen to Kleine Scheidegg?

In one day you could do:
Wengen>Mannlichen>walk to Kleine Scheidegg>Eiger Express down to Grindelwald>First>hike to Bachalpsee
but adding Schilthorn into that isn't realistic.

If Schilthorn is a higher priority and you want to hike, you could do
Wengen>Schilthorn (Wengen-Lauternbrunnen-bus to Stechelberg-Schilthornbahn up to Schilthorn via Gimmelwald, Murren, Birg, Schilthorn) > When you're done at Schilthorn, come back down, but stop at Murren > Northface hike
(if you're there before Oct. 16, take the Allmendhubel funicular and do the hike counterclockwise from Allmendhubel back to the Schilthornbahn before returning from there back to Wengen. If it's Oct. 16 or later, then the Allmendhubel will be closed and you'll have to do the whole thing without the assistance of the Allmendhubel, so if that's too much elevation gain, you could just walk from Murren down to Gimmelwald, walk through the farms and then continue on the Schilthornbahn down before returning to Wengen)

Or a 3rd option, go in the morning to Schilthorn via Lauterbrunnen/Stechelberg and come back to Wengen for an afternoon doing Mannlichen to Kleine Scheidegg. This would be eliminating First/Bachalpsee. You just need to make sure that you return to Wengen early enough to do your walk to KS with enough time to catch the last train return from KS to Wengen.