Water damage to the tenants in 2C and 1C, the building insurance possibly not covered their property loss

You'll probably need a cause and origin report and a coverage attorney to review your policy. Your homeowners' policy insures your property if the cause of loss is covered. Water-related losses have to be carefully sorted against policy language. Your HO insurer does not insure the property of other tenants, although it may include liability coverage for third-party property damage. If you were responsible for the failed pipes, the damaged parties may sue you, and your liability insurer should defend. If someone else owns or is responsible for maintaining the pipes, you can sue them.  But in all of this, you cannot guess at the cause of loss. If it is in dispute, you'll almost certianly need to pay for an engineer's cause and origin report.  Review your insurance portfolio with your agent or broker and get the relevant policies to a coverage attorney.