After an afternoon of rearranging, i think i found the right setup.
on the left, i have Puff, who is an agressive baby who looks like a male. In the middle, i have Fish Sticks (the full grown male betta) and across the divider, Frankie, a baby that i'm not sure the sex of. He is flaring at it, but not as much as he was with the female. Then on the far right i have the female i bought recently. Hopefully this setup will be okay! I'm a college student, so i don't have the space to add more tanks unfortunately :(