Is there any consensus on ethics? What do ethical philosophers do in medical situations? Is there really some ethical training that can objectively tell them when to allow euthanasia or when to allow a certain risky intervention? (if there is we call it laws and regulations)

No, of course not. They're simply highly trusted, generally educated people, who we trust to make roughly okay judgment calls based on their instinct and life experience.

Ethics isn't a field you can study the same way as biology or anatomy. It's about compromises, staying within the broadly socially-culturally acceptible. Sure the moral intuitions of a society do evolve over time and often due to influential philosophers, but I don't think everyday ethics committees tap into anything deep.

It often comes down to an extremely uncertain medical situation where the doctor can provide no useful quantitative probabilities for outcomes and the benefits and risks are really hard to score anyway. So it all comes down to intuition and negotiation and not upsetting the public too much.