How do I quick fill a formula summing an array in a Google Sheets correctly?

Question

I am attempting to make a work-time calculator tool in Google sheet. This consists of one sheet containing a number of projects, each of which contains an (ideally variable) number of sub-projects. Each project is a range of lines, and each sub-project consists of a single line. Each column is a calendar day. The intended use would be to log the amount of time spent on each sub-project each day.

The second sheet is meant to take the times put in for the whole week in each project and sum it, returning the total hours spent on that project each week.

I am running into two issues while doing this:

1. I have no idea of how to go about it having a variable number of sub-project per each project at all

2. Even when using a fixed and equal number of sub-projects per project I can't write a formula that correctly fills in the rest of the spreadsheet. I thought I could just write the formula for one week and then apply it to the whole spreadsheet, but all the others do not apply to the ranges I want them to. So, if the formula for the first week is: =SUM('Sheet1':S8:Y11) I want the formula for the next project in the same week to be: =SUM('Sheet1':S12:Y15) and the formula in the same project for the same week to be =SUM('Sheet1':Z8:AF11) . Instead, I'm getting =SUM('Sheet1':S9:Y12) for the next project in the same week and =SUM('Sheet1':T8:Z11) .

I understand this is probably pretty basic (at least version 2, no idea of version 1), but I do not know the correct terminology to even look up how to do this up on Google. Could you please help, or at least point me in the right direction? Thanks.