Normal practice is to combine the charges and try all charges in one trial.
It's not illegal to schedule 2 trials; it's just (usually) a waste of taxpayer's money.
However, if there are multiple defendants on a particular charge, then it's probably easier to have 2 trials (too confusing to the jury to try multiple charges, multiple defendants).
It's up to the Prosecutor and their office's Policy & Procedures, as to how the charges are filed and tried.