If it don't fit now in time it will, and if it fits an Oscar will try to eat it.
Case in point, lived with them for eight months no harm no foul. Then finally Toni outgrew them and one became dinner
That's a Roseline shark hanging out of her mouth, not a slow fish by any measure. But trapped in a glass box it's only a matter of time.
If you really like puffers, maybe setup a dedicated tank for them... im almost sure you’ll enjoy them more that way compared to if you had to keep separating them coz of fights / problems breaking out in a single tank...