You are required to get a Massachusetts license if you are here for more than 30 days applies to out of state drivers. Foreign drivers are a different story.
An unlicensed charge only carries a $100 fine but may add a license suspension thereby taking away your wife's ability to drive in Mass.
A lawyer in District see cases like this all the time and could probably work out a good deal for you. Any time you go to court you should have a lawyer. If you have never been to court before you...
Unless the court runs your interstate record your Maryland arrest probably will not show up. Even if it does you seem to be eligible for the first offenders disposition. However, the Massachusetts registry will absolutely see your prior offense and they treat you as a second offender even if the court only treats you like a first time offender. Unless you are found to be not guilty you will have to have the ignition interlock device in your car.
Best of Luck
It seems that it is too late to make a payment to the alleged victim. It is probably not the victim that is asking for charges rather the police. If that is the case it can be about more than just the restitution.
If you dad is summons for a clerk's hearing or show cause hearing then the clerk hearing the case may dismiss it on restitution. If it is scheduled for an arraignment the ADA may dismiss it on restitution but it it is unlikely.
Where the assault occurred South Carolina you should follow up the police department that investigated your case. I would suggest you call and speak with either the detective or victim advocate, if you feel you need more information you should contact the District Attorney's Office where the offense occurred. Unless there is a warrant Massachusetts police officers have no reason to investigate the person that assaulted.