Hello Ana,
Thank you for your help but i think that you assumed that i want to filter the post title but i have a field with the first letter of the "family-name" alone so i think it is much easier to filter with the first letter of the "family-name" because in the post title i used the first name before the last name.
What should i change in the code that you have posted to be used on the "family-name" field ?
Many thanks,
Ussama