Isidro also has a sword (which he is too small to use), a smaller sword that he was given by the old man after the group took care of the trolls, the fire dagger, and also he has many things to throw (rocks and those berry things, since i think he used all of the bombs that Rickert gave to Guts) - which is, after all, his talent.
Aside from that, Isidro likely won't be fighting apostles anytime soon. If anything, he'll only try to distract them/hold them while he waits for Serpico or Guts.