Sum data within a date range

Hi think you are a little bit confused.
First of all you have 2 dates. Start and end.
So wich date you want to use to show in the stacked area chart?
If you use the start date the result will be this:

As attachment the pbix.
For the second if you don't explain the way to split the FTE values in week how you can will do it?
Before go in power bi you have to set all the logical rules.
Then with the rules set you can go on power bi to do what you need.
The right visual for your data is wath you have yet built.
If you have a value with a range you have to use the gantt.