Safer to go with 2 pair in the 55 so they can take opposite sides of the tank. On ordinary days 3 pair would work fine, but during spawning times there might be lots of trouble.
It sounds like you will be getting them all at the same time? If so and you purchase them all together, put them all in the 55, let them pair up and see what happens - keep the 25g ready to go in case of trouble...
Just my thoughts...
Cathy