This is where Part cues can be super useful!
Put each fixture (or group of fixtures you want to come on together) in a seperate part of your single cue.
Then set the delay of each part to have them fade in turn with your temp fader.
The relationship between fade time and delay spacing will determine the overlap as they fade.
Cue 1 -Part 1: Fixture 1 @ 100% Fade 2 Delay 0
Cue 1 -Part 2: Fixture 2 @ 100% Fade 2 Delay 1
Cue 1 -Part 3: Fixture 3 @ 100% Fade 2 Delay 2
As you bring the temp fader up fixture 1 will fade up and once it reaches 50% fixture 2 will start fading up, etc etc.
If your fade time was 1 second then fixture 2 would wait until fixture 1 was at 100% to start fading.