Melissa - I can tell you what the updated formats will say for this type of situation. A breve is a breve...so you are correct that the UEB symbol for breve should be used. In many types of material like what you have that I have seen, the other mark looks much more like a grave accent symbol. However, I agree with you that yours appear to be slashes. Whichever print symbol you decide it is, use that braille equivalent (either the slash or the grave accent). What you have done is exactly what we are recommending - with one exception. We are recommending that the symbols be placed over the first letter of the syllable rather than the first vowel as has been done in the past. If you happen to have two small syllables, there does not need to be a space between the two types of accent/stress symbols...and if truly necessary (if the first of two syllables is only one letter) you may place the first accent/stress mark over the space or capital sign that precedes the word.
Let me know if I've not been clear enough. Great job with what you did!