Best way to surprise someone?

My parents-in-law are surprising their daughter by flying across the country in time for their grandson’s first birthday party. The party is at 5 pm on Saturday. They are arriving on Friday night and would like to do the surprising on Saturday morning. Should they just show up on her doorstep unannounced? Should they call first and pretend to still be at home and then ring her doorbell mid-conversation? What scenario would make the best surprise?