Hi GrannyMilly, I am a very new granny so this 'problem' hasn't arisen for me yet, but both myself and my daughter are teachers so our holidays will coincide, However, I would expect her to respect my need for a break as well as trying to be supportive.
I would have thought, if you are trusted with GC overnight that perhaps a 1-2 day assist was reasonable, but especially as this eats into your holiday allowance, more would seem to be unfair.
Do your family apparently 'need' you to cover / babysit for them at half term? If so I can see it must be very hard to say you are unavailable. But they should be respectful of your needs too. Sometimes we think we are the only ones who can help, but if the need arises, other solutions can usually be found.
Hi granny cat you are right I like to,think that I have regular slots with GC and that the D can call,on me for emergencies. Plus I have started to book/plan ahead so that I know where the gaps are in cover and I can step in.