how to install 1 single pole and 1 2 pole GFCI breakers with common #12 neutral
I find it highly improbable that these circuits were wired with /4 cable back in the age when people were using aluminum.  So I will proceed assuming that there is a 12AL/2 cable for the 240V-only pool pump, and a 12AL/2 cable for the pool light/recep.  

12 AWG Aluminum wire requires a 15A breaker. Using a 20A breaker is out of the question. This will be ample for lights/recep and a 1-horse 240V motor.  

I would use a common, 120V, dual-mode AFCI+GFCI breaker on the 12AL/2 cable for the pool light/recep.  That's done and dusted; any GFCI receps on that circuit which are outside can be replaced with plain outlets and used indoors etc. In fact they should be replaced with plain CO-ALR outlets; because most GFCI outlets do not support aluminum wire.  

The reason to use AFCI is the aluminum wire. Small gauge aluminum has a history of problems, but 90% of that is because of using inappropriate receptacles which are not rated for aluminum (or, hastily rated for aluminum with inadequate testing, e.g. "AL-CU" per the 1970s; the R in CO-ALR stands for "revised"). The AFCI takes care of that. 

A 240V, 2-pole GFCI breaker (about $80) goes on the other cable to the pool pump.  The breaker  pigtail goes to the neutral bus, but the neutral terminal on the breaker is unused. 

All aluminum connections should either land on CO-ALR receptacles or switches; or on Alumiconn (mini lug connectors).  If able, a CO-ALR recep makes two aluminum-copper splices and it's cheaper than an Alumiconn. I'm not sure they make 220V receptacles in CO-ALR. 

If the pool pump for any reason has tapped the neutral of the other circuit, you will need to remove that. A normal pool pump does not need it.  If yours is a 120V pool pump, you'll need to rewire that other circuit as 120V instead of 220V, but I doubt that.