Hmm, for boys turning 18? Not sure about gifts, but I might:
- find an old barber who still shaves with a straight razor, and take them in for a guys-guy haircut and shave. Maybe give each a cigar to chew on while sitting there waiting, reading some mags and listening to the old guys talk about man stuff. [you'd have exited, or they'd have driven themselves]
Afterward, a lunch or dinner out where the three of you can relax and talk, about nothing in particular, but with a general celebratory yet calm theme about them becoming men (they're not really yet, but it's a nice thought ). Maybe a personalized letter to each about your reflections about their personality, their early key events or moments, and your hopes and dreams for them in their upcoming lives and years. Something they can read by themselves in private and hold onto. I'd probably write it on heavy bond paper rather than a storebought card. S/t they can hold onto, stick into their bibles for safekeeping.