It's a bit easier with a TSplitter (rather than a TPairSplitter):
Assuming that you want three panels and two splitters. The left splitter should work on the left panel, the right splitter on the right panel, and both splitters always make sure that the center panel adjusts its width so that the entire form width is filled:
- Drop three panels on the form.
- Click the first panel, and make sure that it has Align = alLeft.
- Drop a splitter and set its Align to alLeft as well. Therefore, the splitter should be at the right side of the panel. If not, drag it to that position.
- Click on the third panel, and set its Align to alRight
- Drop the second splitter on the form. Align it to alRight. The splitter should be at the left side of the right panel - if not, drag it to that position.
- Finally click on the third panel and set its Align to alClient
- Done
When you now increase the form width the center panel will change its width. If you drag the left splitter the left panel will change its width, and the width of the center panel will compensate that. And if you drag the right splitter the right panel will change, and the center panel will adjust.
In the same way you can add more "columns". But note that there can only one panel with Align=alClient. So, you must decide which panels will be at the left or right side.
Of course, you can have the alClient panel at the right side of the form; in this case, don't use alRight for the other panel(s) and splitter(s). Or vice versa for the alClient panel at the left.