I've been reading up on clowns, and here's my suggestion. In your 4 ft tank create a nice hiding place at the end o pposite from the black&whites' favourite area. Move the maroon clown to that tank and watch 'em closely. Move the other pair into the 70l tank -- they should be fine. Although the maroon is almost certainy a female, she will be in a new environment with an establised pair and should not be too aggressive. On the other hand, since she is almost certainly a female, she should be aggressive enough to fend off the established pair while she settles in. It will help if you make the nice hiding place very well protected. If there's too much fighting, move the black&whites to your quarantine tank (if you can catch them, sigh) for a few days to let maroon settle. If you can't catch them, add more divinding rock, coral, etc.