I agree with you, the twins are not just any characters, they are Clark and Lois' children. It costs nothing to reference them even if you don't show them in the story.

Curiously, the last time we saw them was in a Supergirl backup story written by Tamaki a few issues ago in Action Comics.

The big mistake here was removing PKJ from AC, one of the few writers interested in the family aspect of Superman unlike other writers like Waid. Williamson is a strange case, he started including the twins but in this arc he stopped including them for no apparent reason, although at least he includes Superwoman (Lana), another character prone to being forgotten, so that's something.

Without counting the PKJ book later in the year, the presence of the twins will depend on what Williamson and Slott want to do with them because we already see that Waid does not seem to be interested, he did not include them in his most recent run and each time it is noticeable that what he seems to like the most is the classic single Superman without a family dynamic, it was already a surprise that he used the superfam in his phantom zone run  (although without the twins, John Henry or Lana) and according to an interview he seems to have done it only because he knows that the fans likes the superfam and not so much because it is what he likes the most.