In that case your boys should be able to. It's genetic.
Liam might be able to - he can curl it, I think Aaron can (his seems to be the most flexible). Justin, however, can't curl his tongue at ALL - just like my mom. Also genetic. :)
My Mom, sister, and I all do clam tongue.
I think my dad could do it - as a kid I remember playing silly games with tongue curling in the car.
Poor Justin - he hates that he's the only one of the boys that can't curl his tongue. :( I tell him he just has a special part of Grammy!