When you say prison, do you mean he is currently on felony probation or facing felony charges. Prison usually only concerns felony charges and convictions. Otherwise if he is facing time behind bars, it is going to be in jail for misdemeanor charges.
A person can violate their probation in a couple ways, usually either by picking up new charges (as with your brothers case), or violating technical terms of probation.
Technical terms are provisions that the court enforces, such as showing up to probation appointments timely, doing classes/rehab as directed, testing positive for drugs or alcohol, or paying fines and court costs.
In your brothers case he will have to fight the charges in order to not be violated. Otherwise, he can probably do a agreed sentence which can cover the new crime and violation of probation. Jail is likely. Having a attorney is a wise choice for your brother.
Your brother's wife wanting to drop the charges does not matter, because it is the State of Florida, specifically the Office of State Attorney, that brings the charges and drops the charges. Most of the time they don't listen to the victims.
Here's where her wishes become a factor. A uncooperative victim is never a good thing for the State. The evidence the State has obviously is a huge factor. Are there pictures, 911 calls or witnesses?
What is going to happen next? There will be new set of hearings for the new charge, and possibly a trial. There will be a Violation of Probation probable cause hearing and possible hearing on the violations.