I left Jerez a while ago so I can set the record straight.
Probation period is 3 months not 6 but it is true that several have not made the grade.
There is a small relocation allowance, not sure of the exact amount currently, and you have free accommodation on site for the first month.
You would need to become tax resident in Spain and be taxed like a national. That does include worldwide assets, property, savings etc. Penalties for not declaring are extremely draconian.
Cost of living dearer than UK in some things, cheaper in others.
Education for kids only in Spanish unless you pay for private and you won't find that locally.
You have full access to the national health system but a lot of people opt for private insurance.
In the last 2 years or so there has been an enormous turnover in staff, so most of the current are relatively new. Prior to that the workforce had been quite stable. As insinuated in a previous post one of the most cited reasons for leaving, including mine, centered around one individual.
Rumours I'm currently hearing suggest pay cuts for some staff, don't know any more than that.
Be pleased to answer any other questions you have.