The first thing you should NOT do is translate the letters yourself! Worst case is the hiring manager (or someone else) contacts your reference and the next communication does not match the tone or language quality as the original. It might appear that you wrote the original (not just translated) or that you 'creatively' translated, or at a minimum that translating was inappropriate. You might ask the instructors to use Google translate to convert their own letter into English, then have another fluent English speaker go over the translation (I've found Google Translate to be fairly accurate, but it's not perfect).
If you're applying for jobs in the US, virtually all managers will be English speaking and may not know a word of Spanish, so a letter in Spanish would be worthless (unless you're applying for jobs in Miami--but even there you might not have a Spanish speaker reading your resume/ letters).
Most times, applicants say, 'references upon request' and that doesn't happen until after an interview. When you're interviewed for jobs point out that you're bilingual, that you know medical Spanish and English and that you studied in a bilingual school and hospital. This is a huge selling point in most of the country--as rusty as my Spanish is (I lived in Argentina for several years) I've found that speaking a foreign language fairly fluently is a tremendous advantage. (This isn't directed at the OP who obviously knows this, but 'fluent' means you can discuss politics, talk about your child's homework or study problems with her teacher, and explain to the mailman that your package didn't arrive yesterday when it was supposed to... fluent isn't just saying, "I have two brothers and a dog") So, play up your ability to speak another language, and as you do it, tell the interviewer that your references speak English as a second language and their letters will be readable but may not be as eloquent or they may seem a bit oddly worded. They certainly should understand this.
Good luck with the job search!