keep going back and forth between scott and sara during my peebee romance playthrough

Not in this game, no. But I previously had to switch gender of the protagonist due to a strong VA and gender appearance preference, and I am really happy when the game does give you this option by offering a bisexual romance. In terms of the cutscene you mention, I will always pick what I see and hear for the entire game vs a few seconds.  an exception would be a romance hack where every cutscene becomes a satire due to animations mismatch, i.e. Qunari and Solas.