Americorp Real Estate
Brokers Associate, e-PRO
Let's put it this way - if you have a mortgage on your condo, you're ultimately responsible for maintaining the insurance. That doesn't mean that the entities that hold title to the other two units do not have obligations, just consider that if they don't pony up, the only recourse the HOA has is "simply" to foreclose, which doesn't help you very much.
If you let the insurance lapse, your lender can slap a minimum-coverage policy (which comes at maximum expense, btw) on the property at your cost.
Buying this condo doesn't have to be the dumbest thing in the world, but you should be getting a deal that makes the risk worth your while.
All the best,