The tenants are responsible for common area maintenance, water and garbage. 

Well, Just like many other homes affected by the freeze in our area, every water pipe in our house burst, causing ten's of thousands of dollars in damages.

Only issue is if you want to sell while construction is going on it might deter a lot of buyers (and renters)The duplex I sold IF I had decided to keep it I probably would have looked at converting it back to a triplex (its configuration probably from about WW2 through early 2000's)  - I would have needed to basically replace a couple walls,   modernize the heating system,   add a third and maybe 4th common electric meter,  and find somewhere (probably a shed) for a common W/D and locate a 3rd/4th water heater.    

Like many homes in our area, our water pipes burst, causing ten's of thousands of dollars in damages.

While I’m in the real estate business as a residential agent, I feel a bit like a fish out of water with multi-family.The main question I have at this point is this: what documents should I be getting from the seller that pertain to the property during this DD period?

They didnt disclose the private water and sewer utility charge.

Pretty much seems to sums it up.A hammer + a nail punch and some tub and tile sealant might work.You don't want water getting under there.Good Luck!

It has its own separate heat & airconditioners with separate controls for each floor, but the utilities are all one electric, one gas and one water bill.

If vacant you need to:what is cost of dumpsters vs buying a pick up or finding some hauler to throw away all the demolition  secure and board up and add cameras, get roof bids, order roof parts, roof needs to get on the house ASAPclean out dry wall, everything fabric throw away, cut up and remove carpet, mop the studs and floor with bleach and water solution (5% bleach), inspect electrical - maybe some shorts or problems, order flooring for kitchen and baths and new kitchen cabinets (measure like you are OCD ten times), how is the sub flooring?

For example, often fire damage is water damage--they put the red stuff out with wet stuff.