You can't. An .ISO file is an image of 1 (one) disk, meant to be used for making 1 (one) disk. You could extract the files from the ISO and put them on 2 disks, using a program like ISOBuster or WinRAR.
Yes, he did. How big is your ISO file? If it is over 4.38GB, then you could always burn the one ISO file to a Dual Layer DVD, which will hold upto 8.5GB of data, provided your burner/software can handle DL burning.