So your pic doesn't show the fwd Grady rodholders but I assume they are 30Deg and angled back 45deg (30 on a 45)
So to fit one between the originals, the Gemlux diagram doesn't help you much. Your "30 on a 45" is already Forward of their 30 on a 45.
You have a choice.
you can put in a 15 on a 45 between them. That will work
You can try to put a 15 where your original forward 30 on a 45 is and then put a 30 on a 45 in the middle. (that is a PIA to move the original.
If you have room in the gunnel toward the bow, you could put the new one FORWARD of the original forward 30 on a 45.
That would be a 15 on a 45 or a 15 straight out(maybe rodtip clearance issue on a hookup)
You would then have room for a ZeroDeg swivel in the middle. ( I use a 0 deg swivel there for fighting with a bentbutt and for drifting for swordfish or deep dropping)
There is no "right way" but there are WRONG ways.
Your main concern is rod tips when trolling. You can't have both at the same angles or the lines will cross.
30deg puts the tip lower than a 15. The "15 on a 45" tip will be higher and Inboard of the "30 on a 45".
My setup is diffent . I added a 30 straight out forward of the original. My express has room in the gunnel to go straight out with a 30 deg. You can't do that.
My 0 deg swivel is between the original grady rodholders.(aft 30 straight back and fwd 30 deg on a 45)
Regarding the cupholder rodholders. They fit the hole but they have a larger flange for the screws. Be certain of clearance if you use an angled rodholder.