The second sentence of the article answers the fake insurance bit; "did not have permission to sell insurance but did it anyway".
If you click the (helpfully underlined) first use of "shadow fleet" in the article it defines it for you. (Or ask Wikipedia; https://en.wikipedia.org/wiki/Shadow_fleet)
I feel like TFA answers the fake insurance question pretty well. The company sold "insurance" which was not actually insurance. They were providing a cover for ships selling from a sanctioned country. Those ships were required to have insurance, and no legitimate business would insure them.
Definitely no. The "fake" here is about certainty that no insurance payout would occur in case of issue, meaning for example an oil tanker accidently dumping tons of black goo onto some english seaside resort, no compensation would come out of anywhere.
Nah. The smaller new ones reinsure via folks like Lloyds. It’s quite complex.
The company in this article could have done that, but they forged documents to avoid it. They had no intention of covering accidents - it was just plain fake to get these ships into ports.