What if you stayed in the room with them and read a book on the floor while they stayed in their beds? That's what we did when our kids started to share a room at that age.
At first glance it sounds like yet another thing that would drag out the bedtime routine. In reality though, if you're spending 2 hours fighting with them, spending 1/2 hour reading a good book on the floor is quite a relief. The rule for us was: If you're in bed and mostly quiet, we stay. If you get too boisterous, we leave. The key for me was to have something else to do so that I was supremely boring. If I'm being boring and they're being quiet in bed, they go to sleep. And some nights, we had some really fun conversations.
When our younger child turned 5, then we began to transition to us not staying. They were older and had much more impulse control then. It also helped that they were both reading, so they started reading themselves to sleep. (We also separated their bedrooms by then.) We started by first cutting down on the time we stayed, then by checking on them in increasing intervals: first 5 min, then 10, then 15, etc. We set the timer on the microwave so they would know that we would come back.