Horse emblem'd. Xander, Cecilia, Reinhardt, and Ursula. Everyone with horse buffs spread around.
After breaking the wall and Xander right behind it, I used my Cecilia (blade+) to one shot the pegasus knight. Afterwards I repositioned her with Xander and with vantage he tanked both Liliana and enemy Cecilia. At that point the enemies are on the other side of the screen and I just picked them off with Ursula. I don't think I needed my Reinhardt except for the horse buffs.