[josu]

This is a solved issue with Merge mining. Here a primer: https://blog.bitmex.com/the-growth-of-bitcoin-merge-mining/

[kenniskrag]

then someone has to mine two blocks?

How are they linked together. E.g. I haven't much luck to mine a bitcoin block and will others put data inside the bitcoin blockchain for me? If it is the other way around there should be some kind of auth?