Luke Thompson and Yerin Ha take the lead on season 4 of ‘Bridgerton,’ revealing secrets to ET about how they pull off filming all the show’s steamy scenes.Plus, there’s romance in store for Ruth Gemmell’s Lady Violet! See what she has to say about getting her own story, too, before binging the first half of the season when it starts streaming, Jan. 29 on Netflix; part 2 drops Feb. 26.