I know many attorneys specialize in one field: family law, criminal law, education law, etc. How difficult is it to have two area of specialities? Would an attorney specialize in constitutional law and real estate law? Is it something that is never done? Is it something that really can’t be done?
Most, but not all, attorneys in the US these days specialize or at least concentrate their practice to a one field or a group of related fields. You might do family law and trust and estates, for example. Or criminal law and constitutional law.
Even in one “field,” there can be a pretty broad scope of practice. Corporate law can be everything from trademark, contract disputes, employment, environmental, etc. Some lawyers really specialize, limiting their field not just to “plaintiff’s tort cases,” but to a particular kind, (medical malpractice, trucking cases, railroad crossings, brain injuries, etc).
Two unrelated specialties would not be too difficult from a practice standpoint, but might be from a marketing and practice development standpoint. Also, there is a flow within a field that might conflict with a different field. For example, criminal cases generally move quickly, 3 to 6 months from the crime to the trial is not uncommon. (Speedy trial and all that). Civil cases plod along at a different pace. If you tried to do both (and some do) you have to be very good at keeping your civil cases moving despite some urgency in your criminal cases. I imagine there could be similar hurdles if you wanted to do any two fields with different cultures and schedules.