There will be two ticket number. You can't put two people on one ticket. KLM should normally have sent one booking confirmation (with both names) and two separate e-tickets.

As for travelling to non-Schengen EU countries using an identity card - absolutely no problem.

National identity cards have been recognised as travel documents since long before the Schengen agreement (and since long before the EU was extended from the original six). If your country was one that issued identity cards then the only time you would need a passport was for travel beyond the Iron Curtain, and for travel outside Europe. ID cards were fine for anywhere in Western Europe, as well as most non-aligned countries (I think Yugoslavia insisted on passports, but places like Austria and Switzerland were certainly ID card territory)