When and if are English-only sound clues effective with kindergartners from Spanish speaking homes? Has this issue been considered/determined? It is too significant to be ignored. Mere assumptions are not good enough!
Notice how long it now takes for these Latino students from Spanish speaking homes to learn to read, to learn their ABCs. Three years is the usual time for them to feel confident about reading, though not really for reading comprehension either.
If the value of English-only examples is not known, why persist? Look elsewhere. Another way to establish most English letter sounds does exist, but not for all 26. ‘W’, ‘H’ and a few other minor letters do require English examples.
Obviously, the many common, shared letters, M, D, R, T, etc. should be learned quickly without bilingual teachers. Just a change to Spanish/English images, T is for TELEPHONE/TELEFONO, etc. will simplify and quicken known letter sound associations.