Setting up a co-prop

Can anyone tell me which companies can set up a co-prop? Roughly how much will it cost? it's a brussels house that has been split into four appartments, there's only building insurance and lighting in the corridors to pay for. I've a feeling (sadly) that the four of us are going to start bickering about splitting the costs, which are only small, so we may have to pay a company to sort out the paperwork, it's actually the law to do this anyway. Anyone any idea how much and who? FR and NL are both no problem but this one's got me stuck.