Faq__kav record1;
Tutorial__kav record2;
Video__kav record 3;

List<Sobject> kbList = new List<Sobject>();

kbliist.add(record1);
kblist.add(record2);

for(Sobject record : kbList){
  if(Sobject is type of FAQ__kav)
     do something...
  else if (Sobject is type of Tutorial__kav)
     do something else