Thanks for your patience. I consulted two other FL experts and we put our heads together. Our thoughts are these: for the TOC, if you are using the bold emphasis on the Spanish, it will be clear to the reader that the non-bold is English. If you didn’t want to use all the bold on Spanish sentences in the TOC, it would be permissible to reverse the emphasis and add it on the English terms. Either way, the emphasis in print (or the one you create) should make it clear to the reader.
As for the accents in other “front matter” materials such as Author/Reviewer lists (oh, I guess you revised your question but I'll answer it anyway), we are suggesting you use UEB modifiers. The Spanish modifiers can be saved for reading/learning portions of the text.