Lauterbrunnen has lockers- for some reason, they no longer specify how many or what size. Look under Equruipment and Mobility at the station.
The left luggage office at Lauterbrunnen is openSlowpoke 0700 to 1900m 7 days per week.
<<"We actually were planning to go by way of mannlichen to Kleine
Scheidegg- Eigergletscher- Alpiglen. We had planned to take the train
from Alpiglen to Wengen. I guess we can take it from Alpiglen to
Grindelwald then Wengen!">>
Yes, you could..
Once at Grindelwald, you could go up and over on the cableways via Männlichen....if it is not too late in the day....or on the train via Zweilütschinen.
Just checked a random day in July. The LSB (Luftseilbahn) from Männlichen to Wengen (Station name is Wengiboden) has its last car down at 1730. The last train via Zweiluetschinen is at 2119 ( 1 hour trip) or a bus at 2219.
Last cograil from LB to Wengen is at 2330.
How had you planned to get from Grindelwald to Männlichen with that routing? It is a 1200 meter climb.
And, last, another option.
This is what I would do. I'd get up early and catch the cableways from GW to Wengen via Männlichen. Leave bags in Wengen. I'd then backtrack by the cable car from Wengen up to Männlichen. I'd take the walks that you planned, and return to Wengen as you planned.
If your bags are to big for the gondolas up from GW to Männlichen, then I'd take the substantially longer route via Zweilütschinen on the trains, get up to Wengen, dump my bags at the hotel or the left-luggage in the station ( 0700 until 1730, every day, no lockers), ride the cableway up to Männlichen, get a cup of coffee and then set out on your original plan.
I'd prefer to get the bags under control first. And, you'll have plenty of time by that route; the cograil runs later than the cableways. Last train from Alpiglen to Wengen vie Kleien Scheidegg is at 1907; via GW, 1947.