We’re not there yet. To me the obvious would be to explain to them something like browsing the internet is similar to being alone in the world’s biggest city and you cannot always be there to protect them whilst online?
I am definitely over simplifying it, but I feel portraying the message that there are good people, bad people and absolutely abhorrent people, is all you can do to protect kids online. Also that everyone takes a big step to the dark side when they are anonymous because for some reason, watching a train crash is more interesting to us that watching one drive past.
I never really thought about controlling screen times for anything other than to make sure kids’ heads spend some time in reality, do you feel it is an effective or important tool for protection too?

We had this at one point too. Turns out they weren’t hungry, so we changed such that the food is there but they choose whether they want to eat. Instead of eating they could bring a piece of paper and do drawing or tell us about their day for a bit while we sit together.
It worked well as it was a lot calmer and the transition to bed wasn’t as big an hour or so later.
Not saying it will work for you, but it helped us.
I don’t have any useful advice for getting them back to sleep on top of the other comments, but for the sanity side of things we found that for us, taking turns was the only way back to sanity.
If you have the option of a couch or a 2nd bed, either you or your partner can sleep there whenever limits are reached. We introduced limited bottle feeds to make this possible at this stage.
A day or two of proper sleep can change lives at this stage.