Ensuring Cell References After Sort

This may be a very simple solution that's I'm missing, so apologies if it is. I'm trying to create a planner which has several project start dates and several tasks for each project. I want the follow up tasks to read the first date, apply a specified working number of days then spit out a resulting day. The problem I'm having is that when I sort the dates, the follow up tasks do not maintain the original references no matter the order I place dollar's or playing around with INDIRECT which to be honest I don't fully understand.

To summarise, I'm just looking for a way to sort the dates column by smallest to largest and for a project's Task's 2, 3 & 4 to read from the relative Task 1, regardless of the order.

I've attached a sheet for clarity

Apologies, forgot the attachment

Hi

As row 2 is an absolute date then you can only sort below that row otherwise all formula other than the original Row 2 are destroyed.

Does that make sense

Cheers

There must be some way around this?