Would the three be financially better off to file separately or together?

Filing as a group or in individual cases won't matter, because most likely the court will consolidate all of the cases together anyway. Once all cases have been consolidate, i.e. all 9, the funds should be divided according to the severity of the injuries, not on an equal basis.

Probably does not matter how you file. If there is negligence the insurance company may likely pay the $100,000 into court and name all the claimant to the pool of money in the suit. If the nine cannot agree on a split, a Judge or Jury will decide what is the $$ allocation.

Simply because the insurance limit is $100,000 does not mean you cannot recover from other assets of the responsibile party(ies). Remember, there may be multiple parties who are liable for the collapse. Therefore, you would have to consider all of their insurance coverages and assets.

If the matter goes through to trial, it may be cheaper (experts, depositions) to sue as joint plaintiffs. The best thing to do is to take advantage of free consultations with several attorneys. They will be able to review the facts to determine what is better in your case.