If you do want to go forward you should have an attorney review the condo docs, rules and regs and financials of the condo associattion even if a 2 unit condo association made up of 2 condexes so you know what you are getting into.
Do you know if they have a mortgage on the place? If so, then most likely each month their lender is escrowing for all this so it should not be a worry.
The town can put a lien on their deed; their portion only- so that whenever the condex gets sold the prop. taxes must be paid first at the closing.
Insurance- that could be more complicated. Because the units are connected, I wouldn't be suprised if your insurance somehhow gets word that they are delinquent and that that half is uninsured. That could present a problem where your insurance company hikes up your rates- thru no fault of your own.
I would say that's all pretty unlikely though...
If you need any help, please let me know. Good luck,