I think there is a way you could do this, but it will be a little bit complicated and you'll have to live with some warning messages.
First, create an extra pipe in your model and for convenience, attach it somewhere near your pump station. The size of it doesn't really matter because it should never convey flow. It can run off to a dead end junction or it can be in parallel like in the picture I've attached. Either way, something is going to be hydraulically disconnected, which will generate yellow warning messages during your runs, but shouldn't affect anything in your model. For good measure, give it 0 slope and set it at the same elevation as the pipe it connects to. To help the logic statements look more sensible, you might name it something like "Large Pump Switch". You're going to use actions to toggle that pipe/switch open and closed so that you can write conditions to see whether you should turn on the little pumps or the big one.
Then you'll need some complex conditions and actions. They should look basically like this:
C1: Tank Level <= 465 AND Large Pump Switch = Closed
C2: Tank Level <= 465 AND Large Pump Switch = Open
C3: Tank Level >=469 AND Large Pump Switch = Closed
C4: Tank Level >=469 AND Large Pump Switch = Open
A1: Pump 1 = On and Pump 2 = On
A2: Pump 3 = On
A3: Pump 1 = Off and Pump 2 = Off And Large Pump Switch = Open
A4: Pump 3 = Off and Large Pump Switch = Closed
Then, write your logic set like this:
IF C1 Then A1
IF C2 Then A2
IF C3 Then A3
IF C4 Then A4
You could probably write just two control statements if you added ELSE clauses, but I found it easier to draw the logic flow up without use of the ELSE clauses.
As I have it set up, the model run starts with the switch closed and Pumps 1 and 2 on and the tank near full. The pumps run until they fill the tank, then turn off and open the switch. When the water level gets to 465, because the switch is open, Pump 3 will turn on. When it has filled the tank, it will turn off and close the switch, so that when the water level gets low again, the two smaller pumps will be turned on and the cycle will begin again. I got warning messages whenever the switch was closed, regardless of whether it was in parallel or a dead end. I think you're going to have to live with that, but maybe someone will have a clever workaround for it.