Amogles:
Answers to your post below in bold green:
Long story, but just a question. If a property is jointly owned by a married couple, and the husband dies, can the widow sell the property before the will is executed? She can sell it by private contract but cannot make the deal a public one with full effects before third parties at the Land Registry. They were already planning to sell the property before he died and possibly the pre-contract was already set up (I don't know). I would have thought his death would have delayed the process but it didn't. I'm confused.
The couple have several adult children. Surely they should be co-owners following the death of their father, but they did not sign the nota simple. Why was this not necessary?
Nota simple is a Land Registry information note. I thiknk you meant escritura ( Notary deeds). In answer to your question: if Spanish Law applies to this deceased person, these children are forced heirs and they can claim their inheritance portion.
http://www.eyeonspain.com/blogs/costaluz/6791/legal-tip-723-free-guide-on-inheritance-law-and-wills-for-dummies.aspx