So pretty much, I found out the following:
1. To use C2, you have to stay within Scirra's terms and conditions -> scirra. com/store/construct-2-personal/personal-license-31
2. Once you want to publish the game you have to comply to terms of the publishing platforms:
Apple -> developer.apple. com/programs/terms/registered_apple_developer_20100301.pdf
Google -> play.google. com/about/developer-content-policy.html
3. To answer my own questions from 1st post:
Scenario a) "I sell the game to a client for 1000$ and later, the client resells the game for 10 000$"
-> I don't need to buy Bussines licence, since I didn't earn more than 5K$, but at the same time, I'm an idiot, and should have sold my game for at least 7K$ (then I would need Business licence)
Scenario b) "I publish the game on friends account, and then share revenue with him"
-> As long as we do not violate publishing platform's terms and conditions, we can publish the game like that, but as soon as I strike 5K$ mark I'm legally and morally obliged to buy Business license
Bottom line, if you make games and plan on making more than 5K$, hire a lawyer and collect all the terms and conditions from all the platforms you plan on using, and give them to your lawyer