Actually, the best step you can take is the first one, having the lawyer in hand. After that we lawyers will have to defer to your counsel. Presumably, the attorney will contact the court which issued the warrant and place the matter on calendar. From there, the case will take the usually criminal procedure steps. You will be arraigned, pre trial discussions will be held. If it doesn't resolve with a deal, then a trial will be set.
Hire and attorney now for your father and follow their advice. Good luck.
The question is why did ICE arrest him? I doubt it's only for a DUI warrant. Is your uncle a citizen or legal resident?
I would counsel against placing too many facts on a public forum like this. You may want to call me. The consultation is free.
This does seem more complicated than most arrest warrant situations since ICE was involved. This suggests there may be an immigration issue involved. You should definitely retain counsel, provide him with full details and follow his advice.
I have never had ICE arrest a client for an old DUI that has gone to warrant status. As others have said, I fear that there could be something's eve serious underlying the case.