It ought to be easy to establish anglicized versions of Spanish names – stress is as important in Spanish as in English, and there are far fewer phonemes in Spanish than in English, so we should be able to find equivalents without too much trouble.
A major difficulty is the assumption that many British people make that they already know how to pronounce Spanish, having spent the obligatory fortnight on one of the Costas. In deciding how to treat a particular name, this leads to preconceptions having to be overcome.
Dealing with stress first, the rules for placing the stress on Spanish words are simple:
1. Words that end in a vowel, or in <n> or <s> are stressed on the penultimate syllable. <i> and <u> next to another vowel do not count as a separate syllable, whereas any combination of <a>, <e> or <o> make two syllables.
2. Words that end in any other consonant are stressed on the final syllable.
3. There are exceptions, but these are all marked by an acute accent placed above the stressed vowel. So, if you know the correct Spanish spelling, then you know where the stress comes.
This is where the problems start: English-language printed material often ignores the accents. Consequently, such triples as cántara (water jug), cantara ((s)he would sing), and cantará ((s)he will sing) become confused. In the case of names, Mérida may be stressed wrongly on the second syllable, and Jaén and Cristóbal on the first.
There is one useful rule of thumb: family names that end in <ez> are stressed on the penultimate syllable, so González, Pérez, Martínez. Jerez, a place name not a family name, is stressed on the final syllable.
The name Esteban, which by all the rules is stressed on the second syllable, is mispronounced by many English speakers who stress the first syllable, even though a little thought would make them realise that it is equivalent to Stephen or Steven.