Without knowing anything about the amp, I'd recommend you play it safe and wire the subs in series for eight ohms.
As you correctly state, the only other option is to wire them in parallel for two ohms but that would be taking a leap of faith that the amp can safely handle this. Are ya feeling lucky, kid?
And, as you again correctly state, there's no way you can wire two four ohm subs and wind up with four ohms. Four, yes, but not two.