What the lowest charge possible for my brother?

The consequences for a drug DUI are the same as those of an alcohol DUI. However, drug DUIs are much harder to prove, because there isn't a specific concentration that the state deems as impairment. With that said, he needs to hire a DUI specialist, because by himself the prosecutor simply won't budge.

Of course he could be found not gullibility- that would be the best. Every case is different. A DUI attorney can often get the possession case dropped and the DUI reduced to a wet or dry reckless.

If he pleads to possession or DUI he loses his license for a year. Fight it.

It depends on exactly what charges are lodged against him, and his criminal history, if any. If it is his first OWI (=DUI) and he is charged in Wisconsin, the offence is only a civil one: no jail, but some ugly forfeiture and surcharges (assume about $950) plus AODA, plus suspension of driving privilege for at least six months. The possession and paraphernalia charges can be treated as local ordinance violations (again, offences but not quite crimes) or as low level misdemeanors. They would likely result in his being sent to Drug Court, a kind of supervision. He needs a lawyer.

With an attorney, he can work a plea deal for the DUI and have the drug charges dropped. Each jurisdiction treats DUI differently, but as a first offense, he could be placed in a diversion program, with no resulting charges.

Informal probation with a fine, community service and an alcohol/drug class.