What are the possible penalties for using your brother's name instead of your own during a DWI arrest with a trooper?

In Utah, like most states, a person commits a class A misdemeanor if, with the intent of leading a peace officer to believe that the person is another actual person, he gives the name, birth date, or address of another person to a peace officer acting in the lawful discharge of the peace officer's official duties.

A class A misdemeanor is punishible by imprisonment for a term not to exceed 1 year and a fine of up to $2,500.

That said, it appears that your brother is facing the charges.  Of course, he will tell the prosecutor it was not him who was driving.  The prosecutor will, most likely, dismiss the charges against your brother, once they find out that you were driving.

Once that happens, the prosecutor will probably file charges against you for the dui and the false information to the peace officer.

I would consult an attorney in your state for further advice.  Until then, I would not turn myself in.  There is a good chance you can resolve this without going to jail.

Hope this helps.