How can you take so much hassle ? 5 days ON 3 days OFF is already way too heavy...Normal should be 4 ON 3 OFF which is fine as long as you don't fly too many legs each day.
Your conditions are the worst in Europe for this business (not considering business operations).
Keep courage and fight. Really !
If you don't react just out of fear of losing passengers, management will understand they can use this type of blackmail any time in the future. You will then think it is better to strike a bit early than striking really hard later on.