The figure 8s/greens require a lot of space, I believe about 10 gallons apiece like goldies. The reason for that is the aggression. Also one other thing to note with the larger puffers is that they need something to keep their beaks worn down or else they'll get too long (like a hamster with nothing to chew on). Ive heard different things about what you can do to wear the beaks down. Giving them hard, pelleted food should do it, but puffers are wild caught and Ive never been able to get mine to eat pellets/flakes. You could also throw some snails in there for them, because chewing on the shells should wear them down, too, and also its a natural food source for them.
Are you planning on keeping them brackish? I believe both of those are true brackish, where others (like mine) are freshwater. Sometimes people convert them to fresh but they never do as well. One other thing on brackish is that they are used to the salinity levels constantly fluctuating like with the natural tides, so varying the salinity a little is a good idea too. Good luck with these guys, I think theyre just adorable fish!!