HOW MUCH JAIL TIME IS HE LOOKING AT ON THE DUI, IF ANY?
If the state has charged his most recent DUI as a felony (Third Offense Within 10 Years), the maximum sentence can be up to 5 years in prison. If it has been charged as a misdemeanor, the maximum jail sentence is 1 year in the county jail.
Is the DUI pending or just the seat belt and suspended license charge? It makes a very big difference. He will undoubtedly be looking at jail time with a 30 day minimum and possibly a year or more if it's a DUI. If the only thing he is presently facing is the seat belt and suspended license charge it is still going to be serious but there aren't "mandatory" minimums. Driving while license is permanently suspended is a third degree felony and is also punishable by up to 5 years prison (the same as the DUI). A lot is going to depend on the prosecutor, the defense attorney, and the judge. If this is Hillsborough county I may be able to help your brother out. Have him give me a call at my website below.
I assume your brother's 4/11 Driving While License Suspended charge springs from his 11/10 DUI. If so, that's not good, for a "DWLS" that springs from a DUI is worse than one that springs from an unpaid ticket, etc.
Worse is his four DUIs in a decade. A prior answer said it depends on whether the 4th DUI has been resolved. If not, and the case ends with a plea or his being found guilty, expect significant jail time in misdemeanor court (if prosecuted as a misdemeanor) - several months at least - even with the subsequent DWLS not being able to be used for purposes of sentencing. Of course, if the DUI is in felony court, the sentence would be worse.
If your brother's 11/10 DUI case is still open and he ultimately prevails at trial, he'll likely still be facing the DWLS, with the state's offer being at least a few months in jail, likely. Of course, the facts of any case is the main factor in what happens with the case, but as noted by a prior answer, the judge, prosecutor, and one's attorney are contributing factors.