If you are looking to purchase say a condex, and there are only 2 units and the other side is not paying their share, you are opening yourself up into a huge liability and stress that you probabily could do without. First thing is usually there is a master insurance policy on the building, it is split bewteen the 2 owners, it could be paid yearly or broken down into monthly payments. If you have a mortgage the mortgage co will demand it is paid and you could be responsible for haveing to pay teh whole thing. Taxes are usually split between the 2 homes and get seperate tax bills, so their tasxes wont affect you. But there should be a long term reserve for say roof repairs or if a common septic and emergencies, that is why monthly payments are recomended.
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.