How is this setup: A 29 gal. tank, 30 lbs live rock, a divider in the middle, with 1 o. mercatoris on each side, 40 lbs live sand, 60 gal. skimmer, and 2 30 gal. filters. no daytime lighting, just a red fluorescent bulb for nighttime viewing. Is it suitable? I'm planning on multiple pvc pipes, and a few table tennis balls along with the shells and rocks for toys.

Hmm...sounds fine, except I would go for a larger tank.

From what other mercatoris keepers are describing, a 29 gallon tank seems adequate. You might try losing the divider--they'll get through it anyway. Since they're not as interactive as some other octos, I'd guess you don't have much to lose (besides one of them) by having them together.

So just lose the divider and hope they get along...sounds good to me!