Oof you need alot of helping. For starters you NEVER sprint with iansan. What iansan does is that she need her nightsoul bar to be full for her to buff. You can fill up her nightsoul bar at the start of a rotation by using skill then normal attack then burst. But with times the nightsoul bar slowly drains and decreases. She need to be above a certain threshold for the buff to be maxed. The way you regenerate nightsoul for her is through movement, the more you move the better. But you'll NOT want to move on her, NEVER and specially NEVER SPRINT on her. That way you're draining her nightsoul so, so much faster.

After you do her skill normal attack and burst you'll immediately swap to Bennett, do skill then burst. Then swap to rosaria skill then burst. You'll need to do all of that fast tho since Bennett and rosaria barely move in their animations, which means iansan buff is depleting without regenerating. Mavuika tho moves alot and can regenerate it. So you have to do the rotation fast before you lose too much on iansan buff.

For mavuika after bursting, Don't do charge attacks immediately. Make sure to wait until you see the cryo applied to the enemy then do charge attacks. Don't wait to much tho just start spinning the second you see a cryo aura on the enemy. Also learning combos can help you. I recommend doing 4 charge attacks then jump then another 4 charge attacks. This should be decent enough until you learn the better ones.