It is always advisable to seek legal advice in the country where the property is located with a view to making a Will and understanding the local tax situation. When making your Will in the UK you should tell your adviser about the property you own abroad.
You should make sure that both your UK Will and your Will abroad complement each other and most particularly that neither cancels (revokes) the other. There is a general rule that a new Will revokes earlier ones and you will need to be careful to avoid this trap.
You will also be able to decide and make an election as to which jurisdiction within the EU should be applied to your Will so that this will determine the law and legal processes to be followed; you may elect, for example, that the UK law should be followed in respect of your Spanish or French Will and not Spanish or French law. This will not however alter the tax position.