It depends on two things:
(a) Exactly what the will says.
(b) Spanish law.
As to (a), it's possible to include language in your will that is not, and is not intended to be, legally binding. You express a hope or a desire that your heirs, or a particular heir, will do X or Y, or will bear Z in mind — "I leave Blackacre to my son X, confident that he will continue the present informal arrangement under which the Donkey Sanctuary uses the upper field when they need it". If the will is in terms like these, then family members won't have a legally enforceable right to use the holiday home; they'll be dependent on the owner to respect the testator's non-binding wishes. But if the will leaves the holiday home to the daughter "subject to the right of each of my other children to have exclusive use of the home for themselves and their families for up to two weeks a year for no payment at a time or times to be agreed with my daughter", that looks a lot like binding language which creates legally enforceable rights that could (in Ireland) be registered as a burden on the land.
If the language of the will is not clear one way or the other, there's potential for a row over whether the rights are legally enforceable, and so are registrable, or not — a row that, ultimately, can only be definitive resolved by court proceedings. So it's important for the testator to be clear in his own mind about what he intends, to have the will drawn up by a professional, and to ensure that the professional understands exactly what he wants and drafts the will accordingly.
If the rights are enforceable and a burden is registered, and the owner later sells the property with the burden still registered, the new owner would still have to make it available for 2 weeks a year to each of the owner's siblings. Which means, of course, that the house is unsaleable unless the burden is discharged, which in turn means heated discussion between the owner and the siblings about exactly what percentage of the sale price each of the siblings will want in order to get them to agree to the discharge of the burden. (Which is precisely the kind of consideration that might make the testator think twice about granting rights of this kind in the first place.)
All that assumes a house in Ireland. Which brings us to (b); things may be different in Spain. I assume, but I don't know, that there is a mechanism in Spain whereby rights in land that fall short of full ownership can be registered, and are enforceable. Assuming that, the questions that arise would be: Is a right to the occasional use of a holiday home the kind of right that is enforceable, and is registrable, in the Spanish system? If so, is the wording of the will sufficient as a matter of Spanish law to create an enforceable, registrable right over this property? If so, whose job is it to register it — the executor who adminsters the will, or the beneficiaries whose right it is? What needs to be done to register it? If it has been registered, how is it enforced? And, if it has been registered, in what circumstances can it be removed and how can that be done? All questions, obviously, on which competent Spanish advice will be needed. Almost certainly the advice will include "make a separate Spanish will dealing with your Spanish property". And this advice will hold even if the testator doesn't want to create enforceable, registrable right — he needs to make a will that, as a matter of Spanish law and practice, clearly does not create those rights.