Yes, there can be 2 chiros under one roof with separate businesses (DBA's). I've done it. I can NOT stress strongly enough, however, how important it is to have EVERYTHING separate. And have a contract outlining who pays for what, and who's responsible for what, under that roof. They will eventually split, and it's easier to split when things are separate.
One doctor can have an "S" corporation (in some states, not in others).
Be especially careful that BOTH docs have liability insurance and malpractice insurance SEPARATELY.
The big wrench comes when they see each other's patients. Be very careful that it gets noted in the patient's file if the other doctor sees them for a particular date of service. If the docs philosophies or treatment ideas or plans or recommendations differ, MAKE NOTES. This can bite you in the butt if the patient decides to sue later. Doesn't happen often, but there is always the possibility. If they are going to see each other's patients, have some sort of Informed Consent signed showing that the PATIENT agreed to see the other doctor.
There are complications when sharing a front door, but it can be done. You just have to spell things out clearly, and don't let the docs get their feelings hurt by pointing out ALL the possibilities. Problems can go both ways, protect both sides!