Voadam
Legend
Have you talked to them about it?
This was my thought. "Hey guys, I want to try to keep the pace of combat a bit brisker, one thing that would help would be rolling dice together instead of one at a time on your turns. Thanks."
Depending on the number of people in your group I might add "Because we have so many people I want to cut down the wait time between people acting in combat so people aren't just sitting around so much."
Structurally I would keep the NPCs and pets and summoned monsters and such to a minimum so it is generally just one quick PC action each and the monsters go round to keep it quick paced and more personally focused.