Izabella, your step-grandchildren will probably find your stories about your travels far more interesting than falsely cosy attempts to bond by reading sacharine books to them.
There isn't a certified list of what you should or shouldn't do, for any grandparents, let alone step ones, except that it is a bad move to set up in oppostion to their established relationships. Be yourself, be interesting, don't boss them around, don't criticise their parents but be available as an alternative adult for them to turn to should you be needed.