We have booked a chalet about 2 kilometers south of the train station in Lauterbrunnen. Will there be either taxi or Uber service available at the train station?
I do not know if anyone waits there, but this is a local taxi service that you could contact and book a pickup
Or this garage in Stechelberg apparently offers taxi service. You can contact them using the form on their webpage.
Uber is not a thing there and taxis would need to be pre-arranged. Is there a bus stop near your place?
have you asked the host which is the nearest bus stop to them and how far it is? There is really only one road between Stechelberg and Lauterbrunnen and if 2 km out of Lauterbrunnen it must be near it. Near the vending machine on the main road or the one across the river on the lane? Certainly before Trummelbach Falls. Either way, not far from a bus stop. The bus is a yellow Postbus with plenty of room, and they are used to folks with luggage and or bicycles. Runs every 30 minutes. I mention this because I wouldn't want you relying on taxis for the whole time.