How many puffers?

GSPs need at least 30 gallons per fish, so ideally a 25 gallon is really too small for even 1 GSP. You could, however, keep 1 figure 8 puffer in a tank as small as 15 gallons. I probably wouldn't try to keep 2 F8's in a 25 though.
 
Actually, 15g for the 1st F8 & 10g for every one after that, so a 25g would be perfect for 2 F8s.
 
AquariaCentral.com