ILS26,
I would be interested to know what you are referring to ? You say crews work "over legal hours" what do you mean ? Crews can work longer than the FTL table limits if the Captain excercises discretion. This may allow for anything up to an additional 3 hours on the planning FTL limits. That is not illegal. FTL can be a complex subject and it is worth reading your companies operations manual from time to time, so that you are better aware of what is permissable in various situations. I would be the first to admit that the subject can be difficult, but I doubt that crews are actually working illegally, since it would fall squarely on the captains shoulders in most instances. Few captains are easily intimidated. Of course any extension of a duty period should require a corresponding increase in the subsequent rest period.
Being "fit to go on duty" is normally a decision for the individual. If you feel you are not fit, then you phone in sick. Of course sickness does often put pressure on the crewing department which in turn falls back on the remaining crew. If you fly when unfit to do so, then you are in violation of the rules and of course it is then you that are operating illegally. operating while off duty is of course not possible, since you would be on duty. Working on a planned "day off" is also not illegal provided the overall limits as laid down in the FTL scheme are not violated. Normally it is up to the individual to agree to surrender such a day.
I do appreciate that in the real world there is often considerable pressure applied to work beyond the planned limits often at short notice. In reality there is a good deal of flexibilty in the companies FTL schemes as agreed with the authority, that permits this. Obviously it is not acceptable to undertake any duty that is actually outside the rules and it is incumbent on both the operator and the crewmember to ensure this does not happen. In my experience few crewmembers and particularly cabin crew do take the trouble to properly understand the rules. If you are in any doubt ask. If you are not satisfied ask the operating Captain ( before departure).
Finally, any real violation is not acceptable. If this happens then you can certainly report the matter to the authority, or if you wish to CHIRP, the confidential reporting body at Farnborough. I have to say though that I would be very surprised if an operator was electing to act outside of the law. Usually the real problem is an individuals perception of what the law actually is.