Make excel data work harder/better for small restaurant chain

We run 3 restaurants (with 2 more on the way)

The restaurants fill in daily sales sheets individually that are currently saved on dropbox.

Id like the restaurants to enter simple information also for the number of hours the staff work. Could be drop down boxes for each name, and then a start and finish time, which then calculate the number of hours worked and adds them up centrally. Id want to see each staff allocated to a group

Waiting staff
Administrator
Kitchen
Pizza
Cleaning


Currently we manually take the information from the sales sheets to do any forecasting.

I would like the sales spreadsheets to work together, bringing all the information in one place, so that I can see all sales together, and compare, daily, weekly, monthly trends. Id like to see this information in simple charts also.

We have our own server that could host any centralised files or software.

I would be open to any other ideas that you may have. In fact. I would encourage it.